Hi !
We had the same error. Our solution was reviewing the SQLNET.ORA file updating the "SQLNET.AutentificationServices" parameter puting it from "NTS" to "None".
We hope it work for you too.
We began using DOA 3.4.3 for Oracle 8.1.6 access. No problem. But we changed to Oracle 8.1.7 and we've got troubles about "Access Violation". We now already have DOA 3.4.5 for using with Oracle 8.1.7. Are both version's compatible? Do I need anything else to make them work together?