well, here is my original post, now that this isn't in the unban request section XD
You say you seem to be banned from EVERY CE server? Or just the BFM CE server? If it is all, then this would probably fit better in the tech support and chat section. (which it now is)
When you installed CE, did you use the CD key that originally came with the Halo disk that you own, or did you obtain a different key somewhere else? Or did it not ask for a CD key?
Also, you say it is only on the servers that use maps that you've downloaded? Try going into a server with an original map, such as timberland, bloodgulch, or infinity, although I doubt it is the maps.