Just installed Forge 3.1.2.90 with MC 1.2.5...I have several other mods installed (and they were installed in the order which they are listed in the report), all of which were checked to be in working order immediately after their installation...so I'm certain that Forge has caused the crash, somehow. Any help would be greatly appreciated 

And of course, the report.

 

 

Mods loaded: 10

ModLoader 1.2.5

mod_Arrows 1.2.5

mod_Biosphere 1.2.5

mod_ClayMan 1.2.5 v.7

mod_Gulliver 0.7.1 (MC 1.2.5)

mod_ModLoaderMp 1.2.5v1

mod_Shelf 1.2.5

mod_SpawnerGUI 1.2.5

mod_TooManyItems 1.2.5 2012-04-13

mod_MinecraftForge 3.1.2.90

 

      Minecraft has crashed!     

      ----------------------     

 

Minecraft has stopped running because it encountered a problem.

 

 

 

 

--- BEGIN ERROR REPORT 588cd878 --------

Generated 7/1/12 11:34 AM

 

Minecraft: Minecraft 1.2.5

OS: Windows 7 (amd64) version 6.1

Java: 1.7.0_05, Oracle Corporation

VM: Java HotSpot 64-Bit Server VM (mixed mode), Oracle Corporation

LWJGL: 2.4.2

OpenGL: ATI Radeon HD 5670 version 4.1.10750 Compatibility Profile Context, ATI Technologies Inc.

 

java.lang.NoSuchMethodError: mm.<init>(IZ)V

at mod_Arrows.load(mod_Arrows.java:89)

at ModLoader.init(ModLoader.java:891)

at ModLoader.addAllRenderers(ModLoader.java:189)

at ahu.<init>(ahu.java:77)

at ahu.<clinit>(ahu.java:

at net.minecraft.client.Minecraft.a(Minecraft.java:394)

at net.minecraft.client.Minecraft.run(Minecraft.java:732)

at java.lang.Thread.run(Unknown Source)

--- END ERROR REPORT b9e9509d ----

java.lang.NoSuchMethodError: mm.<init>(IZ)V

at mod_Arrows.load(mod_Arrows.java:89)

at ModLoader.init(ModLoader.java:891)

at ModLoader.addAllRenderers(ModLoader.java:189)

at ahu.<init>(ahu.java:77)

at ahu.<clinit>(ahu.java:

at net.minecraft.client.Minecraft.a(Minecraft.java:394)

at net.minecraft.client.Minecraft.run(Minecraft.java:732)

at java.lang.Thread.run(Unknown Source)

--- END ERROR REPORT b9e9509d ----

Actually, as you can see, it is crashing in some arrow mod, that is the culprit.  Specifically it is calling an invalid method on the ItemBow class, which indicates that something other than Forge is installed in to the Minecraft jar.  Make sure that only Forge has anything in the Minecraft jar.