It seems like it has something to do with the latest update, seeing as how everything worked fine till the new update. Can't even play unless on the new snapshot, which has no sound at all.
Same problem here. I'm on windows xp and gives me the error like above. Like everyone else only the new snapshot works, but no sound. Worked fine this morning between 3 and 5.
Play on 1.7.10,
Hope this gets resolved soon...
Edit: Did try deleting and reinstalling both Minecraft and java, along with deleting all Minecraft files. No luck.
Can confirm that MultiMC 5 works. Used it for the first time today, glad I did. I can play again 🙂