zomg thats so unfair !!1!1!1!
Hmmm. That happened to me too after removing the Newbies team. Must be an issue with teams.txt.
Well, save your bots and overwrite your old Teams folder with a new, fresh copy of it (with just The Newbies on it).
Ah, and if you must reinstall RA2, be sure to have another "virgin" copy of RA2, that you will only use as a backup for copying files.