Hmm...I belive quite a while ago (like almost a year ago) there was some bug with JJM servers which messed up on downloading some levels, you could try finding those levels in your cache and deleting them. Also, another reason that this can happen is when the user saves their level in jcs, but hasn't reset their level yet on their server. I'm not sure what else can cause this though.

Ohh! And another thing. Some TSF servers have multiversion on but are hosting a TSF only level, ending up in this error too if you join with 1.23 I think.