I just downloaded BF2 yesterday and when I try to join into your and some other servers I get ban message?! I wonder why I get this message "you have been banned from the server by a server admin...etc" although I never used cheats?!

You are using a license key that is publicly available hence it is probably already banned on most of the servers (because somebody else already used it and cheated on it, most likely).

Regards,
Staff Officer S_h_a_r_k_93