Anyone ever encounter the following message when trying to book a hotel room via iDine?

GUE7: EXPIRATION DATE INVALID, PLEASE CORRECT
SYS81: SYSTEM ERROR, UNABLE TO PROCESS


I've emailed iDine and they say online system is working fine -- can't give me an explanation for the error message -- not even what it means. I've used the same credit card with the same expiration date for the past year -- no problem. The iDine rep encouraged me to just reserve the hotel via phone , but I hesitate to do that just yet.

Suggestions?