Minecraft Forums

So I recently installed Forge and it worked perfectly fine. But after a week it doesnt work. When i click play, forge just closes and gives me this crash:

Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release
[10:42:36] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[10:42:36] [main/INFO] [LaunchWrapper]: Using primary tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[10:42:36] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLTweaker
[10:42:36] [main/INFO] [FML]: Forge Mod Loader version 7.10.25.1207 for Minecraft 1.7.10 loading
[10:42:36] [main/INFO] [FML]: Java is Java HotSpot(TM) 64-Bit Server VM, version 1.8.0_20, running on Linux:amd64:3.13.0-35-generic, installed at /usr/lib/jvm/java-8-oracle/jre
[10:42:36] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[10:42:36] [main/INFO] [LaunchWrapper]: Loading tweak class name cpw.mods.fml.common.launcher.FMLDeobfTweaker
[10:42:36] [main/INFO] [LaunchWrapper]: Calling tweak class cpw.mods.fml.common.launcher.FMLInjectionAndSortingTweaker
[10:42:36] [main/ERROR] [LaunchWrapper]: Unable to launch
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901) ~[?:1.8.0_20]
at java.util.ArrayList$Itr.remove(ArrayList.java:865) ~[?:1.8.0_20]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:117) [launchwrapper-1.9.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.9.jar:?]

I use Ubuntu 14.04.

I had the same problem when I upgraded to Java 1.8.0_20, I was using Java 1.8 until that point. Just install Java 7 alongside or as a substitute and everything will work again.

Thanks