Today I tried to start playing a singleplayer world using a few mods. No matter what I try, the launcher will disappear, only to instantly reappear. I've tried updating Java (v1.7.0_57 to v1.8.0_31) to no avail. It says something about a FML plugin being unable to configure at http://pastebin.com/NWLhEndJ. Any help? NOTE: This occurs for every version of Forge (1.6.4, 1.7.2/10, 1.8)
If you want to be able to run and switch between multiple profiles each running different game version and different mods, you gotta learn how to use the profiling in the new launcher:
http://www.minecraftforum.net/forums/support/modded-client-support/tutorials-and-faqs/525478-tut-ucs-launcher-multiple-modded-profiles-like