It's difficult to tell what might be wrong from what you describe. I suggest you uninstall, remove your configuration file, reinstall the program, and try to open the data file from your last known good backup.
Hopefully, by "backup" you mean a copy of the database which you know worked and which you have not attempted to open since the time you know it worked. Attempting to open a database with the wrong version of the program can corrupt it. If your backup was made with the internal backup feature of an older version of the program, I'm not sure if it can be restored by a newer version. I suppose it won't hurt to try, but you may have to install the old version it was created with, restore the database, then update the program.
The error you're getting, it would seem the program is attempting to update the database to a new format, but is unable to do so. This would happen if the database was corrupted by, perhaps, trying to open it using an older version of the program than the one that created or last used it. Since you tried to open it with 0.9.7.1, it's particularly important you revert to the last known good backup.
It's possible the problem has something to do with the OS and how Firebird files are handled. It seems odd you would "switch" from 7 to XP. Are you talking about the same machine? Have you ever installed the server version of Firebird?
