This is a warning that a few days ago, a Java update versioned 1.8.0_20 was released, which currently makes it impossible to play modded Minecraft. The release fixed a Java bug which was hiding a bug in Forge Modloader- users with this new version of java will now receive a ConcurrentModificationException when trying to load modpacks in Minecraft 1.6+.
Forge is currently working to correct this issue, but in the meantime, we advise that you do not update your Java version to 1.8.0_20. We...
ConcurrentModificationException in Java 1.8.0_20
Forge is currently working to correct this issue, but in the meantime, we advise that you do not update your Java version to 1.8.0_20. We...
ConcurrentModificationException in Java 1.8.0_20