I received my paper statement today (9/20/10) which said my next payment is due on 10/8/10. I used Quicken and Bill Pay to send a payment ASAP and apparently it picked 9/24/10 for the check. Discover rejected the check with an OL-297-A error which can be: Server down or a firewall problem or ...... OR check can't be collected by the payment due date(!) which they said was tomorrow (9/21/10). My guess is Discover was using last month's due date rather than the current one. Of course, Discover would not confirm or deny this.
So, watch out for late fees and fines from Discover.