A friend of mine had this problem and I don't remember exactly what he did but I think he unlinked his gamertag, then did something in-game and then re-linked it, and it solved the problem.

I think he had to actually select all his custom classes in-game while it was unlinked.

I guess this process kicked the server in the nuts, kuz it worked ok after that.

Give it a shot - let people here know if it worked