Crash on startup

For some weird reason, whenever i try to boot up the new snapshot, I get this crash message. I have deleted it, and installed it again, but it still doesn't work.

The game crashed whilst initializing game
Error: com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Invalid escape sequence at line 4 column 30 path $.pack.description

I don't know what this means, sooo...