The PRM file is usually the one to change to solve this. You need to restrty the connection server once you have changed the prm file for the Oracle database.
If that still does not work, then there is this check list to go through. The PRM file change is also detailed there:-
https://bobj-board.org/t/84923
Mak 1 
(BOB member since 2005-01-06)