Hi Jeff,
I haven't seen anything like that using 8.1.6 or 8.1.7. You might want to make sure that NDS or some such isn't causing the problem. Also you might want to check out your authentication setting (in sqlnet.ora) You might want SQLNET.AUTHENTICATION_SERVICES= (NTS) or
SQLNET.AUTHENTICATION_SERVICES= (NONE)
Hope that helps!
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Mark Ford
Benthic Software
Quality Oracle Tools