More details:

Database A Oracle 8.1.7 (server 1) Listerner 10g
Database C Oracle 9.2.0 (server 1) Listerner 10g

Database B Oracle 9.2.0 (server 2) Listerner 10g


1. Login to A as sqlplus / and using Dblink to B - Ok.
2. Login to A as sqlplus user@A and using Dblink to B - Fails
3. Login to C as sqlplus user@A and using Dblink to B - Ok.

In shot using db link while login via client fails from 8.1.7 database.

Thanks in advance