We have a multithreaded, multi-tier server which uses ODBC
(ODBCExpress/Delphi Easysoft Driver) for our connection to Firebird (among
others (SQL Server, AS400, Oracle, etc.)

I found I received that error mostly when the Firebird I was trying to
connect to was on a machine other than the one our multi-tier server was
running on, so much so that it is a requirement for our product to have our
server and Firebird on the same machine.

I do not have this problem when any other database.