Whenever I launch minecraft in 15w37a, The blue download bar will get almost to the end, jump around a bit, and finally it will close the launcher. It will reopen again less than a second later, and the bottom part will briefly say "Already Playing." an error message will then display-

Error: Could not find or load main class net.minecraft.client.main.Main
Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release

This was a problem for me about 2 weeks ago, but then it would only work about a fifth of the time. It was fixed, but now it happens all the time in the new snapshot, 15w37a. This appears to be on my end, but could you still tell be how to fix it?