Before performing the connection, the program first

> tries to find ("if FileExists") the file (if I give it a direct path,
> not an alias), and in this case it reports successfully having found
> the database file (which, indeed, does appear in the Z folder, as it
> should).

Read my response again. I explicitly tell you NOT to put the fdb file
in the data folder on the main computer. Your alias should not point
to a mapped drive, but the real location of the file on disk as seen
by the main computer.

10061 is a winsock error message. It is probably telling you that your
firewall is blocking Firebird. Did you create an exception in your
Windows firewall? Are you 100% sure the service is running (check task
manager)

Adam