“ODBC Firebird Driver Your username and password are not defined” error message

There is a good chance that the Firebird service is not running. To check this:

1. To start a service, open services.msc
2. Locate the Firebird service and make sure the status shows as running. 
3. If it was blank (not running), right click on the service and select start.

If this is not the problem, check the ODBC database path to make sure it is connected to the correct server as described in this article Client Payroll Manager is working slow and seems to be sluggish.