Fatal NI connect error 12560, connecting to:

Hello,

I have a VB front end program that connects to an Oracle backend db.
Nothing has changed on either end; however, when I try to connect to
the db via VB program I receive a requires OLE DB Session Object. The
SQL error I receive is:

 Tns error struct:
    nr err code: 0
    ns main err code: 12560
    TNS-12560: TNS:protocol adapter error
    ns secondary err code: 0
    nt main err code: 530
    TNS-00530: Protocol adapter error
    nt secondary err code: 126
    nt OS err code: 0

I can connect to this database via SqlNet. What did change was my
Oracle Registry relating to NLS_LANG which I unfortunately changed to
UTF8 to try to fix another program in another db. Anyway, I basically
had to delete all the Oracle stuff in the registry and reinstall
Oracle client 9.2. Again, I can connect to the db via sqlnet. The db
ver is 8.0.4

Any ideas would be much appreciated.

Many thanks