When this happens, it usually means your NWN CD keys have changed. Are you trying to play from someone else's installation?
We had to implement this sort of security to compensate for the NWN Master Login Server being taken offline several months ago. Without this protection, then anyone who knew your username could login to your account, as passwords ceased to be checked when the login server went offline.
If you can switch back to your original CD keys, you should once again be able to play. If you can't switch back, then you will need a DM to clear your account lock. Once cleared, your account will be locked to the CD keys next used to login with your username.
