I'm going to guess this is related to the same thing that caused the error noted by curbcrusher in the original "We Miss Seeing You Onboard" Emails.

The last digit of most (or all?) RR numbers is a check digit. Promotion registration routines were recently revamped. The routines that formerly processed Emailed registration links did not use the check digit. (It isn't needed; your RR number is already unique without it). The problem with the originally Emailed links was that, as in the past, they did not include the check digit. Unfortunately the new routines were written to expect the check digit to be included. So if you are eligible for the Chase offer and receive a name mismatch error like toomanybooks did when trying to register at http://southwest.com/exclusiveoffer/, give it another try without the last digit of your RR number. (This may already have been fixed, however.)