Dion,

I had this error when I used a wrong connection-string.
Check your HOST file for correct IP´s,
Check your SERVICES file for an entry 3050 gds.
Check your connection string, for the TCP/IP protocol
it has to be
SERVERNAME:SERVER_DRIVE\SERVERPATH\DATAFILE.GDB
e.g.
Your server is named : Firebirdserver
Your path on the Firebirdserver is :
E:\Firebird\Data\xyz.gdb

---> Connection string is :

Firebirdserver:E:\Firebird\Data\xyz.gdb

Don´t use mapped drives or unc-path names.

Check it for *ALL* your clients and don´t mix it up.

If you access your server direct (local) then use

localhost:E:\Firebird\Data\xyz.gdb
or
127.0.0.1:E:\Firebird\Data\xyz.gdb

to force the tcp/ip protocol.

HTH
Achim