Actually it seems you are correct.

/me slaps self in forehead, I had installed a Firebird while
Interbase Server (ibserver.exe) was still running - so the
ibserver.exe and gds32.dll files were not replaced resulting in a
corrupt installation.

You would not believe the frustration this has caused me! I think I'm
going to get some sleep - I think I need it!

B.J.Tolputt