>SqlState = 28000
>Your user name or password are not defined

I think this indicates that the password is something else than masterkey (or that someone has created a role called sysdba, something that prevents logging in as sysdba). I know that on some systems Firebird generates a different password upon installation (although I didn't think it did so on Windows) and saves the password in a file. Take a look at the release notes.

HTH,
Set