Subject ODBC connection: 'gds32.dll' failed to load

This is a "connection failure via ODBC"-issue, I hope I've chosen the appropriate group.

A windows service of mine, which is running on a Windows Server 2003 R2 (64-bit) and connecting to a remote Firebird database via ODBC, is throwing the following error since I installed a newer version of my service:

ERROR [08004] [ODBC Firebird Driver] Unable to connect to data source: library 'gds32.dll' failed to load

It's stunning that the way I'm connecting to the Firebird database did not change in the newer version of my service. I'm (still) using the Firebird_ODBC_2.0.0.148 driver and DB-Version My connection string (still) is:
(I've created an alias named WIEN)
In ODBC driver manager, when I test the dsn, I also get the above error.

I've tried to take the fbclient.dll of the Firebird server, rename it to gds32.dll and copy it into the System32 and System-directories of the Windows 2003 server. Unfortunately that didn't help.
The "instclient q g" command gives the following output:
"Installed GDS32.DLL version : (shared DLL count 2)"

Any recommendations are highly appreciated!
Thanks a lot,