Pb connexion distant oracle database using QOCI

Hello everyone,
I've developped an application which must connect to an Oracle database installed on a distant server.
I've encourtred a problem with when I try to connect to my database from a client on which I've installed Oracle 8 and Oracle 9 client.
The error is QOCI : Unable to logon.
I've modified the local tneNames file and I can connect to my database using sqlplus.
Can anyone have an idea about this problem and tell me what I must to do to resolve this problem.
Many thanks in advance.
Best regards.