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my forge is not working the launch code this is

Aug 22, 2014 6:30:15 PM net.minecraft.launchwrapper.LogWrapper log
INFO: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
Aug 22, 2014 6:30:15 PM net.minecraft.launchwrapper.LogWrapper log
INFO: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
Aug 22, 2014 6:30:15 PM net.minecraft.launchwrapper.LogWrapper log
INFO: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
2014-08-22 18:30:16 [INFO] [ForgeModLoader] Forge Mod Loader version 6.4.49.965 for Minecraft 1.6.4 loading
2014-08-22 18:30:16 [INFO] [ForgeModLoader] Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_20, running on Windows 8.1:amd64:6.3, installed at C:\Program Files\Java\jre1.8.0_20
2014-08-22 18:30:16 [INFO] [ForgeModLoader] Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
2014-08-22 18:30:16 [INFO] [ForgeModLoader] Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
2014-08-22 18:30:16 [INFO] [ForgeModLoader] Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
2014-08-22 18:30:16 [SEVERE] [ForgeModLoader] Unable to launch
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.remove(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:114)
at net.minecraft.launchwrapper.Launch.main(Launch.java:27)
Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release

plz help

I have the same problem as op, I reverted to java 7 but got the same result.

EDIT: Nevermind, I saw that I had not uninstalled the development kit, deleted it. Works now.

Thanks, this is something easy to miss.

Quote from dsh666»

hi, this is 1st time ive ever used any kind of forums but ive unistalled java 8 and installed 7 and totally remove all mincraft stuff (ie:versions profiles mods, all that) and I still cant launch it heres my error message.....

Encountered similar problem just now. I fixed it by opening "Edit Instance" to the right, checking the Java Installation box and choosing Java 7.

Download the JavaLegacyFixer mod and put it in the mods folder. The one file works for just about every version.