Forge or mods not working

[Aeriona]

Hello, I've never used this forum site before, and I know little to nothing about code. 

This morning I downloaded some mods that required Llibrary, which i promptly downloaded. It worked for a while, but whenever I try to open a save the game crashes and displays this message:

The game crashed whilst exception in server tick loop
Error: java.lang.NoSuchMethodError: net.minecraft.entity.EntityLiving$SpawnPlacementType.canSpawnAt(Lnet/minecraft/world/World;Lnet/minecraft/util/math/BlockPos;)Z

And here's the detailed crash report:

java.lang.NoSuchMethodError: net.minecraft.entity.EntityLiving$SpawnPlacementType.canSpawnAt(Lnet/minecraft/world/World;Lnet/minecraft/util/math/BlockPos;)Z
    at net.minecraft.world.WorldEntitySpawner.func_180267_a(WorldEntitySpawner.java:226)
    at net.minecraft.world.WorldEntitySpawner.func_77191_a(WorldEntitySpawner.java:282)
    at net.minecraft.world.gen.ChunkGeneratorOverworld.func_185931_b(ChunkGeneratorOverworld.java:466)
    at net.minecraft.world.chunk.Chunk.func_186034_a(Chunk.java:1019)
    at net.minecraft.world.chunk.Chunk.func_186030_a(Chunk.java:999)
    at net.minecraft.world.gen.ChunkProviderServer.func_186025_d(ChunkProviderServer.java:157)
    at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:344)
    at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:173)
    at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:196)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
    at java.lang.Thread.run(Thread.java:745)

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

-- System Details --
Details:
    Minecraft Version: 1.12.2
    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: 467778192 bytes (446 MB) / 872415232 bytes (832 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
    IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
    FML: MCP 9.42 Powered by Forge 14.23.5.2847 Optifine OptiFine_1.12.2_HD_U_C6 5 mods loaded, 5 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 | cfm       | 6.3.1        | MrCrayfishs-Furniture-Mod-1.12.2.jar | None      |

    Loaded coremods (and transformers): 
    GL info: ~~ERROR~~ RuntimeException: No OpenGL context found in the current thread.
    Profiler Position: N/A (disabled)
    Player Count: 0 / 8; []
    Type: Integrated Server (map_client.txt)
    Is Modded: Definitely; Client brand changed to 'fml,forge'

What does it mean? How to I fix this?

It may have something to do with OptiFine, which I downloaded just before it broke. 

[DaemonUmbra]

The filenames of one or more of your mods suggests you got them from a repost site.

Please read up on the StopModReposts project (link in my signature) for info on why this is a bad thing.

[Aeriona]

Ok, thank you.