It's not your problem.  It's a bug in the game.  Read the forums, there are other people with the same issue.

Try rebooting your computer or try hosting a game instead.

Had the same yesterday, with several games. Today it's working perfectly, though.

And about the different error messages, I agree, there should be more clarifications. For instance, I suspect I got kicked from a game yesterday. Don't know why, the creator only said "..." and some things that didn't quite make sense, then I got some message about abandoning the lobby. But when I pressed OK and the games refreshed the game was still up with 3 people in. Kind of confused about what exactly happened there.