Remove RM2K3 completely.
Go to your Start Menu and click on 'Run'. Type in 'regedit' without the quotes.
Click the HKEY_CURRENT_USER folder. Then the software folder, then the Enterbrain folder, then delete the RPG2003 folder. Then reinstall RM2K3. If this doesn't work then I don't know.
There may also be one in HKEY_LOCAL_MACHINE\Software\Enterbrain. If there is, delete it.