Yea, same problem here
-- BEGIN ERROR REPORT 1f2e317e --------
Generated 10/27/13 12:04 PM
Minecraft: Minecraft 1.2.5
OS: Windows 7 (x86) version 6.1
Java: 1.7.0_45, Oracle Corporation
VM: Java HotSpot Client VM (mixed mode), Oracle Corporation
LWJGL: 2.9.0
OpenGL: GeForce 9500 GT/PCIe/SSE2 version 3.3.0, NVIDIA Corporation
java.lang.IllegalArgumentException: Slot 241 is already occupied by codechicken.enderstorage.BlockEnderChest@5e7733 when adding ic2.common.BlockRubSapling@1e3cd0d
at pb.<init>(Block.java:251)
at qk.<init>(SourceFile:11)
at qk.<init>(SourceFile:19)
at zc.<init>(SourceFile:19)
at ic2.common.BlockRubSapling.<init>(BlockRubSapling.java:24)
at mod_IC2.load(mod_IC2.java:224)
at cpw.mods.fml.common.modloader.ModLoaderModContainer.init(ModLoaderModContainer.java:356)
at cpw.mods.fml.common.Loader.modInit(Loader.java:273)
at cpw.mods.fml.common.Loader.initializeMods(Loader.java:628)
at cpw.mods.fml.client.FMLClientHandler.onLoadComplete(FMLClientHandler.java:223)
at net.minecraft.client.Minecraft.a(Minecraft.java:429)
at net.minecraft.client.Minecraft.run(Minecraft.java:738)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT d9436265 ----------