Unable to fit: missingno (what does it mean?)

Sorry if 1.7.10 isn't supported, but i'm having trouble with forge version 1614. I just wanna play around with Clay Soldiers (alongside other mods for no reason), put them in an arena, etc. And i'm planning to use WorldEdit to make it easier. But, every time, it gets to the Texture Stitching, It Crashes. If i should post this Elsewhere, let me know please. Thanks!

Crash Report:
 

---- Minecraft Crash Report ----
// Everything's going to plan. No, really, that was supposed to happen.

Time: 10/12/19 1:15 AM
Description: Registering texture

net.minecraft.client.renderer.StitcherException: Unable to fit: missingno - size: 16x16 - Maybe try a lowerresolution resourcepack?
    at net.minecraft.client.renderer.texture.Stitcher.func_94305_f(Stitcher.java:76)
    at net.minecraft.client.renderer.texture.TextureMap.func_110571_b(TextureMap.java:260)
    at net.minecraft.client.renderer.texture.TextureMap.func_110551_a(TextureMap.java:97)
    at net.minecraft.client.renderer.texture.TextureManager.func_110579_a(TextureManager.java:89)
    at net.minecraft.client.renderer.texture.TextureManager.func_110580_a(TextureManager.java:71)
    at net.minecraft.client.renderer.texture.TextureManager.func_130088_a(TextureManager.java:58)
    at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:545)
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:878)
    at net.minecraft.client.main.Main.main(SourceFile:148)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    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 --
Stacktrace:
    at net.minecraft.client.renderer.texture.Stitcher.func_94305_f(Stitcher.java:76)
    at net.minecraft.client.renderer.texture.TextureMap.func_110571_b(TextureMap.java:260)
    at net.minecraft.client.renderer.texture.TextureMap.func_110551_a(TextureMap.java:97)

-- Resource location being registered --
Details:
    Resource location: minecraft:textures/atlas/blocks.png
    Texture object class: net.minecraft.client.renderer.texture.TextureMap
Stacktrace:
    at net.minecraft.client.renderer.texture.TextureManager.func_110579_a(TextureManager.java:89)
    at net.minecraft.client.renderer.texture.TextureManager.func_110580_a(TextureManager.java:71)
    at net.minecraft.client.renderer.texture.TextureManager.func_130088_a(TextureManager.java:58)
    at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:545)

-- Initialization --
Details:
Stacktrace:
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:878)
    at net.minecraft.client.main.Main.main(SourceFile:148)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

-- System Details --
Details:
    Minecraft Version: 1.7.10
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_51, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 144926744 bytes (138 MB) / 369098752 bytes (352 MB) up to 2147483648 bytes (2048 MB)
    JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
    IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
    FML: MCP v9.05 FML v7.10.99.99 Minecraft Forge 10.13.4.1614 11 mods loaded, 11 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
    UCH    mcp{9.05} [Minecraft Coder Pack] (minecraft.jar) 
    UCH    FML{7.10.99.99} [Forge Mod Loader] (forge-1.7.10-10.13.4.1614-1.7.10.jar) 
    UCH    Forge{10.13.4.1614} [Minecraft Forge] (forge-1.7.10-10.13.4.1614-1.7.10.jar) 
    UCH    Micdoodlecore{} [Micdoodle8 Core] (minecraft.jar) 
    UCH    sapmanpack{2.7.2} [SanAndreasPs Manager Pack CORE edition] (SAPManPack-1.7.10-2.7.2.jar) 
    UCH    claysoldiers{2.0.0-beta.2} [Clay Soldiers Mod] ([Minecraft-INSIDE.com] clay-soldiers-mod-1.7.10.jar) 
    UCH    BiomesOPlenty{2.1.0} [Biomes O' Plenty] (BiomesOPlenty-1.7.10-2.1.0.1548-universal.jar) 
    UCH    GalacticraftCore{3.0.12} [Galacticraft Core] (GalacticraftCore-1.7-3.0.12.504.jar) 
    UCH    GalacticraftMars{3.0.12} [Galacticraft Planets] (Galacticraft-Planets-1.7-3.0.12.504.jar) 
    UCH    ExtraPlanets{1.7.10-2.1.2} [Extra Planets] (ExtraPlanets-1.7.10-2.1.2.jar) 
    UCH    worldedit{6.1.1} [WorldEdit] (worldedit-forge-mc1.7.10-6.1.1-dist.jar) 
    GL info: ' Vendor: 'ATI Technologies Inc.' Version: '4.5.13469 Compatibility Profile Context 21.19.526.1026' Renderer: 'AMD Radeon(TM) R2 Graphics'
    Launched Version: 1.7.10-Forge10.13.4.1614-1.7.10
    LWJGL: 2.9.1
    OpenGL: AMD Radeon(TM) R2 Graphics GL version 4.5.13469 Compatibility Profile Context 21.19.526.1026, ATI Technologies Inc.
    GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

    Is Modded: Definitely; Client brand changed to 'fml,forge'
    Type: Client (map_client.txt)
    Resource Packs: [vanilla]
    Current Language: English (US)
    Profiler Position: N/A (disabled)
    Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
    Anisotropic Filtering: Off (1)