ORA-12638: Credential retrieval failed

You may hit this error during connecting your database by using 3th party tools such as Toad etc.

You are hitting this error If the Oracle client was installed using the domain administrator account instead of the local administrator.

To solve this error follow below steps:

1. open  your LOCAL sqlnet.ora file
2. Search for  SQLNET.AUTHENTICATION_SERVICES= (NTS) and change it to –> SQLNET.AUTHENTICATION_SERVICES= (NONE)
3.  Save file and retest issue.

If issue persist than you can try below syntax:

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)