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PROBLEM: Encountered ORA-12638 Credential Retrieval Failed error when attempting to make SQLNet connection from client to Oracle 9.2.0.6 database server across a network using Windows 2003 Active Directory servers.
SOLUTION: Commented out the following line in the client machine's sqlnet.ora file:
#SQLNET.AUTHENTICATION_SERVICES= (NTS)
REFERENCES: Various forums found by googling ORA-12638
ADDITIONAL INFORMATION: Posted on the OTN Forums:
ORA-12638: Credential retrieval failed
Cause
The database and client always cross authenticate each other if NTS authentication is negotiated.
This is regardless of whether the user will ultimately be authenticated by the database using a user name and password or OS credentials. NTS authentication happens at the start of the handshake. For NTS authentication to succeed both the client OS user and the database server must be in the same domain or in two domains which trust each other.
Solution
Either create trust between the two domains or change the client or server SQLNET.AUTHENTICATION_SERVICES such that NTS in not negotiated in the connection handshake. NTS is only negotiated if both client and server have SQLNET.AUTHENTICATION_SERVICES set to NTS.
http://forums.oracle.com/forums/thread.jspa?threadID=345365&tstart=0