(Forge version is 1.12.2) I guess some people already had this problem but my is unique. Everything is fine until I press next button in inventory. Its the one that moves you to mod categories (< and >). So yeah when I press that button, game freezes and few seconds later shows message: Shutting down internal server. After it, crash log shows this: 

Spoiler

---- Minecraft Crash Report ----

WARNING: coremods are present:
  weaponlib (mw-1.11.7.7_mc1.12.2.jar)
Contact their authors BEFORE contacting forge

// I bet Cylons wouldn't have this problem.

Time: 2/11/20 2:55 PM
Description: Rendering item

java.lang.IllegalStateException: Not building!
    at net.minecraft.client.renderer.BufferBuilder.func_178977_d(BufferBuilder.java:537)
    at net.minecraft.client.renderer.Tessellator.func_78381_a(SourceFile:21)
    at com.vicmatskiv.weaponlib.compatibility.CompatibleWeaponRenderer.func_188616_a(CompatibleWeaponRenderer.java:137)
    at net.minecraftforge.client.ForgeHooksClient.renderLitItem(ForgeHooksClient.java:653)
    at net.minecraft.client.renderer.RenderItem.func_191967_a(RenderItem.java:118)
    at net.minecraft.client.renderer.RenderItem.func_191961_a(RenderItem.java:106)
    at net.minecraft.client.renderer.RenderItem.func_180454_a(RenderItem.java:149)
    at net.minecraft.client.renderer.RenderItem.func_191962_a(RenderItem.java:308)
    at net.minecraft.client.renderer.RenderItem.func_184391_a(RenderItem.java:347)
    at net.minecraft.client.renderer.RenderItem.func_180450_b(RenderItem.java:336)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_147051_a(GuiContainerCreative.java:922)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_146976_a(GuiContainerCreative.java:758)
    at net.minecraft.client.gui.inventory.GuiContainer.func_73863_a(GuiContainer.java:75)
    at net.minecraft.client.renderer.InventoryEffectRenderer.func_73863_a(InventoryEffectRenderer.java:51)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_73863_a(GuiContainerCreative.java:643)
    at net.minecraftforge.client.ForgeHooksClient.drawScreen(ForgeHooksClient.java:396)
    at net.minecraft.client.renderer.EntityRenderer.func_181560_a(EntityRenderer.java:1124)
    at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:1119)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:398)
    at net.minecraft.client.main.Main.main(SourceFile:123)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Client thread
Stacktrace:
    at net.minecraft.client.renderer.BufferBuilder.func_178977_d(BufferBuilder.java:537)
    at net.minecraft.client.renderer.Tessellator.func_78381_a(SourceFile:21)
    at com.vicmatskiv.weaponlib.compatibility.CompatibleWeaponRenderer.func_188616_a(CompatibleWeaponRenderer.java:137)
    at net.minecraftforge.client.ForgeHooksClient.renderLitItem(ForgeHooksClient.java:653)
    at net.minecraft.client.renderer.RenderItem.func_191967_a(RenderItem.java:118)
    at net.minecraft.client.renderer.RenderItem.func_191961_a(RenderItem.java:106)
    at net.minecraft.client.renderer.RenderItem.func_180454_a(RenderItem.java:149)
    at net.minecraft.client.renderer.RenderItem.func_191962_a(RenderItem.java:308)

-- Item being rendered --
Details:
    Item Type: com.vicmatskiv.weaponlib.Weapon@277c10c2
    Registry Name: mw:m16a4
    Item Aux: 0
    Item NBT: null
    Item Foil: false
Stacktrace:
    at net.minecraft.client.renderer.RenderItem.func_184391_a(RenderItem.java:347)
    at net.minecraft.client.renderer.RenderItem.func_180450_b(RenderItem.java:336)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_147051_a(GuiContainerCreative.java:922)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_146976_a(GuiContainerCreative.java:758)
    at net.minecraft.client.gui.inventory.GuiContainer.func_73863_a(GuiContainer.java:75)
    at net.minecraft.client.renderer.InventoryEffectRenderer.func_73863_a(InventoryEffectRenderer.java:51)
    at net.minecraft.client.gui.inventory.GuiContainerCreative.func_73863_a(GuiContainerCreative.java:643)
    at net.minecraftforge.client.ForgeHooksClient.drawScreen(ForgeHooksClient.java:396)

-- Screen render details --
Details:
    Screen name: net.minecraft.client.gui.inventory.GuiContainerCreative
    Mouse location: Scaled: (412, 132). Absolute: (824, 696)
    Screen size: Scaled: (640, 481). Absolute: (1280, 961). Scale factor of 2

-- Affected level --
Details:
    Level name: MpServer
    All players: 1 total; [EntityPlayerSP['Smederevac'/760, l='MpServer', x=-219.06, y=80.00, z=253.83]]
    Chunk stats: MultiplayerChunkCache: 961, 961
    Level seed: 0
    Level generator: ID 06 - BIOMESOP, ver 0. Features enabled: false
    Level generator options: 
    Level spawn location: World: (-220,64,240), Chunk: (at 4,4,0 in -14,15; contains blocks -224,0,240 to -209,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
    Level time: 355 game time, 355 day time
    Level dimension: 0
    Level storage version: 0x00000 - Unknown?
    Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
    Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
    Forced entities: 93 total; [EntityCreeper['Крипер'/4132, l='MpServer', x=-167.50, y=22.00, z=236.50], EntityChicken['КокоŃ�ка'/73, l='MpServer', x=-273.50, y=64.00, z=285.50], EntityChicken['КокоŃ�ка'/74, l='MpServer', x=-276.50, y=64.00, z=284.50], EntityChicken['КокоŃ�ка'/75, l='MpServer', x=-279.50, y=64.00, z=282.50], EntityChicken['КокоŃ�ка'/76, l='MpServer', x=-279.50, y=64.00, z=280.50], EntityZombie['Зомби'/4172, l='MpServer', x=-264.50, y=19.00, z=244.50], EntityPig['Свиња'/77, l='MpServer', x=-269.50, y=73.00, z=314.50], EntityPig['Свиња'/78, l='MpServer', x=-274.40, y=74.00, z=323.21], EntityPig['Свиња'/79, l='MpServer', x=-267.50, y=71.00, z=315.50], EntityPig['Свиња'/80, l='MpServer', x=-264.57, y=70.00, z=323.23], EntityCow['Крава'/81, l='MpServer', x=-275.50, y=76.00, z=320.50], EntityCow['Крава'/82, l='MpServer', x=-276.50, y=75.00, z=320.50], EntityCow['Крава'/83, l='MpServer', x=-276.50, y=75.00, z=320.50], EntityCow['Крава'/84, l='MpServer', x=-273.50, y=74.00, z=320.50], EntityPig['Свиња'/85, l='MpServer', x=-250.01, y=66.00, z=296.46], EntityPig['Свиња'/86, l='MpServer', x=-249.09, y=66.00, z=297.23], EntityPig['Свиња'/87, l='MpServer', x=-248.31, y=66.00, z=295.83], EntityPig['Свиња'/88, l='MpServer', x=-244.76, y=66.00, z=299.28], EntityZombie['Зомби'/4184, l='MpServer', x=-235.50, y=30.00, z=256.50], EntityPig['Свиња'/89, l='MpServer', x=-232.50, y=70.00, z=306.50], EntityZombie['Зомби'/4185, l='MpServer', x=-235.50, y=30.00, z=255.50], EntityPig['Свиња'/90, l='MpServer', x=-235.50, y=67.00, z=304.50], EntityPig['Свиња'/91, l='MpServer', x=-234.50, y=67.00, z=302.50], EntityPig['Свиња'/92, l='MpServer', x=-234.50, y=67.00, z=305.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4193, l='MpServer', x=-282.50, y=21.00, z=267.50], EntityPig['Свиња'/104, l='MpServer', x=-234.26, y=66.00, z=244.46], EntityPig['Свиња'/105, l='MpServer', x=-228.49, y=65.00, z=236.90], EntityPig['Свиња'/106, l='MpServer', x=-226.53, y=67.97, z=242.65], EntityPig['Свиња'/107, l='MpServer', x=-229.56, y=65.00, z=239.12], EntityItem['item.tile.mushroom.glowshroom'/108, l='MpServer', x=-228.49, y=27.00, z=254.79], EntityItem['item.tile.mushroom.glowshroom'/109, l='MpServer', x=-230.21, y=27.00, z=256.39], EntityPig['Свиња'/110, l='MpServer', x=-229.50, y=72.00, z=309.50], EntityPig['Свиња'/111, l='MpServer', x=-225.50, y=75.00, z=311.50], EntityPig['Свиња'/112, l='MpServer', x=-224.62, y=76.00, z=314.55], EntityPig['Свиња'/113, l='MpServer', x=-225.51, y=77.00, z=316.31], EntityPig['Свиња'/114, l='MpServer', x=-205.80, y=63.00, z=265.79], EntityPig['Свиња'/115, l='MpServer', x=-202.50, y=65.00, z=258.72], EntityPig['Свиња'/116, l='MpServer', x=-217.83, y=65.00, z=267.83], EntityPig['Свиња'/117, l='MpServer', x=-212.50, y=63.00, z=270.50], EntityItem['item.tile.rail'/131, l='MpServer', x=-169.88, y=27.00, z=227.88], EntityItem['item.tile.torch'/132, l='MpServer', x=-176.75, y=23.00, z=255.01], EntityMinecartChest['Колица Ń�Đ° ковчегом'/133, l='MpServer', x=-178.50, y=23.06, z=249.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4229, l='MpServer', x=-243.50, y=19.00, z=241.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4230, l='MpServer', x=-241.50, y=19.00, z=239.50], EntityPig['Свиња'/136, l='MpServer', x=-168.50, y=64.00, z=331.50], EntityPig['Свиња'/137, l='MpServer', x=-168.50, y=64.00, z=331.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4237, l='MpServer', x=-283.50, y=62.00, z=297.50], EntityCreeper['Крипер'/4272, l='MpServer', x=-150.50, y=27.00, z=232.50], EntityCreeper['Крипер'/4322, l='MpServer', x=-221.50, y=31.00, z=266.50], EntityCreeper['Крипер'/4324, l='MpServer', x=-272.50, y=30.00, z=268.50], EntityCreeper['Крипер'/4328, l='MpServer', x=-256.50, y=22.00, z=273.50], EntityZombie['Зомби'/4347, l='MpServer', x=-138.50, y=24.00, z=292.50], EntityCreeper['Крипер'/4363, l='MpServer', x=-230.50, y=18.00, z=207.50], EntityZombie['Зомби'/4364, l='MpServer', x=-235.50, y=18.00, z=207.50], EntityZombie['Зомби'/4366, l='MpServer', x=-236.49, y=17.00, z=214.24], EntityZombie['Зомби'/4386, l='MpServer', x=-251.50, y=48.00, z=212.50], EntityZombie['Зомби'/4403, l='MpServer', x=-212.50, y=19.00, z=173.50], EntityZombie['Зомби'/4412, l='MpServer', x=-225.50, y=29.00, z=248.50], EntityWitch['ВеŃ�тица'/4413, l='MpServer', x=-231.34, y=31.00, z=247.75], EntityWitch['ВеŃ�тица'/4414, l='MpServer', x=-226.50, y=29.00, z=250.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4417, l='MpServer', x=-297.33, y=64.00, z=294.50], EntityCreeper['Крипер'/4440, l='MpServer', x=-142.50, y=27.00, z=250.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4455, l='MpServer', x=-247.50, y=46.00, z=202.50], EntitySpider['ПаŃ�Đş'/4463, l='MpServer', x=-256.50, y=17.00, z=264.50], EntityCreeper['Крипер'/4483, l='MpServer', x=-272.50, y=19.00, z=263.50], EntityZombie['Зомби'/4485, l='MpServer', x=-236.50, y=47.00, z=222.50], EntityWitch['ВеŃ�тица'/4486, l='MpServer', x=-233.50, y=47.00, z=220.50], EntityWitch['ВеŃ�тица'/4487, l='MpServer', x=-234.50, y=47.00, z=218.50], EntityCreeper['Крипер'/4537, l='MpServer', x=-275.57, y=35.13, z=215.69], EntityBat['Слепи миŃ�'/4692, l='MpServer', x=-221.67, y=21.58, z=174.47], EntityPlayerSP['Smederevac'/760, l='MpServer', x=-219.06, y=80.00, z=253.83], EntityBat['Слепи миŃ�'/1855, l='MpServer', x=-288.85, y=26.95, z=277.30], EntityBat['Слепи миŃ�'/2971, l='MpServer', x=-221.47, y=46.03, z=219.87], EntityBat['Слепи миŃ�'/3039, l='MpServer', x=-274.42, y=40.86, z=202.50], EntityZombie['Зомби'/3103, l='MpServer', x=-207.50, y=26.00, z=233.50], EntityBat['Слепи миŃ�'/3147, l='MpServer', x=-204.57, y=27.54, z=235.81], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/3882, l='MpServer', x=-228.29, y=23.00, z=197.51], EntityBat['Слепи миŃ�'/3883, l='MpServer', x=-274.58, y=36.44, z=216.52], EntityBat['Слепи миŃ�'/3906, l='MpServer', x=-215.61, y=29.26, z=321.20], EntityCreeper['Крипер'/3929, l='MpServer', x=-234.50, y=65.00, z=289.50], EntityZombie['Зомби'/3946, l='MpServer', x=-263.49, y=20.00, z=247.27], EntityZombie['Зомби'/3983, l='MpServer', x=-250.50, y=30.00, z=222.50], EntityBat['Слепи миŃ�'/3985, l='MpServer', x=-167.42, y=38.11, z=313.69], EntityBat['Слепи миŃ�'/3989, l='MpServer', x=-201.01, y=21.34, z=178.50], EntityItem['item.tile.gravel'/4003, l='MpServer', x=-257.13, y=47.00, z=206.24], EntitySpider['ПаŃ�Đş'/4005, l='MpServer', x=-224.50, y=26.00, z=293.50], EntitySkeleton['КоŃ�Ń‚Ń�Ń€'/4017, l='MpServer', x=-233.50, y=47.00, z=184.50], EntityItem['item.tile.gravel'/4034, l='MpServer', x=-258.88, y=47.00, z=208.88], EntityCreeper['Крипер'/4037, l='MpServer', x=-188.50, y=58.00, z=291.50], EntityCreeper['Крипер'/4047, l='MpServer', x=-270.50, y=24.00, z=258.50], EntitySpider['ПаŃ�Đş'/4048, l='MpServer', x=-273.50, y=24.00, z=260.50], EntityZombie['Зомби'/4062, l='MpServer', x=-153.50, y=33.00, z=185.50], EntityItem['item.tile.gravel'/4071, l='MpServer', x=-258.13, y=47.00, z=208.70]]
    Retry entities: 0 total; []
    Server brand: fml,forge
    Server type: Integrated singleplayer server
Stacktrace:
    at net.minecraft.client.multiplayer.WorldClient.func_72914_a(WorldClient.java:420)
    at net.minecraft.client.Minecraft.func_71396_d(Minecraft.java:2741)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:419)
    at net.minecraft.client.main.Main.main(SourceFile:123)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

-- System Details --
Details:
    Minecraft Version: 1.12.2
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_151, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 310157280 bytes (295 MB) / 1060372480 bytes (1011 MB) up to 1060372480 bytes (1011 MB)
    JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
    IntCache: cache: 0, tcache: 96, allocated: 0, tallocated: 0
    FML: MCP 9.42 Powered by Forge 14.23.5.2847 10 mods loaded, 10 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored

    | State  | ID            | Version      | Source                                        | Signature |
    |:------ |:------------- |:------------ |:--------------------------------------------- |:--------- |
    | LCHIJA | minecraft     | 1.12.2       | minecraft.jar                                 | None      |
    | LCHIJA | mcp           | 9.42         | minecraft.jar                                 | None      |
    | LCHIJA | FML           | 8.0.99.99    | forge-1.12.2-14.23.5.2847.jar                 | None      |
    | LCHIJA | forge         | 14.23.5.2847 | forge-1.12.2-14.23.5.2847.jar                 | None      |
    | LCHIJA | aether_legacy | 1.4.4        | aether_legacy-1.12.2-v1.4.4.jar               | None      |
    | LCHIJA | atum          | 2.0.15       | Atum-1.12.2-2.0.15.jar                        | None      |
    | LCHIJA | biomesoplenty | 7.0.1.2441   | BiomesOPlenty-1.12.2-7.0.1.2441-universal.jar | None      |
    | LCHIJA | lucky         | 7.6.0        | luckyblock-1.12.2-7.6.0.zip                   | None      |
    | LCHIJA | mw            | 1.11.7.7     | mw-1.11.7.7_mc1.12.2.jar                      | None      |
    | LCHIJA | mystcraft     | 0.13.7.03    | mystcraft-1.12.2-0.13.7.03.jar                | None      |

    Loaded coremods (and transformers): 
weaponlib (mw-1.11.7.7_mc1.12.2.jar)
  com.vicmatskiv.weaponlib.core.WeaponlibClassTransformer
    GL info: ' Vendor: 'ATI Technologies Inc.' Version: '4.6.13559 Compatibility Profile Context 26.20.12028.2' Renderer: 'Radeon RX550/550 Series'
    Launched Version: 1.12.2-forge1.12.2-14.23.5.2847
    LWJGL: 2.9.4
    OpenGL: Radeon RX550/550 Series GL version 4.6.13559 Compatibility Profile Context 26.20.12028.2, ATI Technologies Inc.
    GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

    Using VBOs: Yes
    Is Modded: Definitely; Client brand changed to 'fml,forge'
    Type: Client (map_client.txt)
    Resource Packs: 
    Current Language: СрпŃ�ки (СрбиŃ�Đ°)
    Profiler Position: N/A (disabled)
    CPU: 4x Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz

And yes Ive tried deleting certain mods but it still didnt worked. Please anyone help!

1.12 is no longer supported due to age.

In order to receive support on this site, please update to a modern version.

 

See the LTS link at the top of every page for more information.

1 minute ago, Ugdhar said:

1.12 is no longer supported due to age.

In order to receive support on this site, please update to a modern version.

 

See the LTS link at the top of every page for more information.

But my latest version is 1.12.2 in titan launcher and I theres no option to update it.