If you get a message like: 'Dynamic SQL Error SQL error code = -901 feature is not supported', this may be caused by InterBASE client 6.01 accessing a server running 5.x.
Make sure the dialect value is set to '1', like the following:
ibase_connect ('localhost:/usr/db/db.gdb', 'SYSDBA', 'masterkey', 'ISO8859_1', '100', '1' ) ;
That last value is the dialect, but you need the two preceding also, do avoid errors.
Anthony