Working on some Ant scripts and Oracle today and out of the blue I get this error:

ORA-12638 credential retrieval failed

Everything was working yesterday!  I restarted Oracle and my workstation – no luck!  Argh.

A quick Google however turned up a simple solution – simply modify your sqlnet.ora file. On my machine running Oracle XE this is located:

C:\oraclexe\app\oracle\product\10.2.0\server\NETWORK\ADMIN

And change one line:

Original Entry – SQLNET.AUTHENTICATION_SERVICES= (NTS)
Modified Entry – SQLNET.AUTHENTICATION_SERVICES= (NONE)

After I changed this I tried it and it worked – no reboot, restart required!  Reading on the Oracle forums – apparently the “NTS” option tries to use your Windows credentials to authenticate with Oracle.  So unless your Oracle logins match your Windows login – this may fail.