My friend had the same error last night but it was only on some servers not all. Do you have any modded skins or guns? That could possibly be an issue im not sure. We just kept picking servers till we got some that let us in.
Ok well since noone else wants to help, what we found was that after replacing our config file ,scripts, alias's, skins, and basically everything else it still happened on afew servers. So im not sure if it means the server is running an older version than you or what bad it let him in to almost every other server.