>What I usually do in all the tests I conducted was:
>
>turn off Firebird server on the SERVER computer turn off my program on the CLIENT computer
>Copy the database to the SERVER with a normal copy from a usb drive.
>turn on firebird server on the SERVER computer Launch my program on the CLIENT computer

Sounds OK, but as an additional security, you could rename the database file before you tried to copy it (if something is connected to it, then it is likely to give an error message).

>during launch I can see a progress bar in my program so I know when the connection is working
>or not, and when it reaches around 60% I get the error

Do you know that the program has connected to the Firebird database? A way to test would be to see if you can connect directly to the database from isql (comes with Firebird, textbased), FlameRobin (www.flamerobin.org, more graphical than isql and I think it is freeware) or some similar tool.

If you still have problems connecting, maybe we need to see your connect string (and your actual error message - I've seen 335544...-codes before, but don't remember what each of them are). Typically, Firebird doesn't connect through shares. Also, make sure your operating system (OS) never backs up the Firebird database (run gbak to make backup and then let your OS back up the backup it creates). Moreover, I wonder if some OS actually first copied the file when you tried to open it from certain locations, and that's not wise to do with database systems like Firebird.

If all else fails, you could try Firebird 2.5 and look at the monitoring tables (isql/flamerobin) during startup of your program. Maybe that can show you what your program is trying to do (I think monitoring tables also were available in 2.1, but that they've been improved with 2.5 - Thomas can confirm or deny that, he knows them very well).

HTH,
Set