Installer will not accept a zero in the registration number.

The Interbase 7.1 installer will not accept a zero in the registration number.

Correct. Neither the number "0" nor the letter "O" are used in order to avoid confusion between the two. (Similarly, the number "1" and the letter "l" are not used.)

If you have a "registration number" that has a zero in it, it is very likely that this is actually a license number. The registration number can be found on a label on the CD case containing the InterBase 7.1 CD.