I'm using the advanced integration method.

I've been processing transactions in production successfully for a year, but as of 11/17/2011, I get a response code of 103 with a message of "This transaction cannot be accepted.".

I tried getting a new transaction key but that didn't make a difference.  I'm pretty sure nothing has changed on my end.  My code still works when using the test sandbox.  Is there anything I can do differently to troubleshoot this problem?