Can't play Minecraft 1.9?

I keep getting the
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
message. How do I fix this? Nothing I've seen online works, and this only happens for 1.9 snapshots and newer. Everything 1.8.9 and older still functions just the same.