I applied this plug-in to my Magento store and used it successfully to process a test transaction. After processing I logged into our account at the Test Business Center at Cybersource and saw that the transaction had been received in good order. So that all seemed to work just fine.
But then, when I then went back to Magento and set Test Mode = No for this payment method and tried it for a live payment of 1.00, I get back the following error message:
Gateway request error:
Security Data: UsernameToken authentication failed.
I know that our Cybersource account is active because I have captured a test transaction through their (live) Virtual Terminal.
UPDATE: (Woops, never mind.)
It never fails. As soon as I finally yell for help I always seem to figure it out myself 5 minutes later. In this case, the problem seems to have been that you need to generate a new Transaction Security Key in the (live) Business Center and paste that into Magento when you’re’ ready to go live. A key generated in the Test Business Center apparently works only for the test site. Seems pretty obvious in retrospect so I feel a little dumb, but I will leave this post up anyway on the chance that it could help someone else.