Originally posted by rajabalachandra
oracle documentation does not cover this error.
Oh yes, it does. However, you must look under TNS-12638, not ORA-12638.

http://download-west.oracle.com/docs...us.htm#1002603
TNS-12638 Credential retrieval failed

Cause: The authentication service failed to retrieve the credentials of a user.

Action: Enable tracing to determine the exact error.