OK... thanks to your little description there, i started playing with those files. MY BOARD NOW WORKS!
Here is exactly what i did.
1. uploaded all my old cgi from 547
2. deleted /cgi-bin/Members/public_names.cgi (so the upgrade will run again)
3. uploaded the whole modules folder to /cgi-bin/
4. ran /cgi-bin/ubb6_upgrade.cgi
After that, the registration problem went away.
PL