catwood,

I had the same problem when using an AWD different from the one in my profile(i.e no preferred service...). I followed the advice posted on this thread and have never had the problem since.

http://www.flyertalk.com/forum/Forum77/HTML/000136.html

The recommendations by others are good. I have had success using a coupon with a different(non-corresponding) AWD code. FWIW, the cheapest rate I could find for my two upcoming rentals is the AWD# D002807 with the $25 off weekend coupon previously mentioned.