Can anyone explain why a legitimate AWD cannot be used with a President’s Club Wizard number?

I am attending a conference and the conference organizers have provided a conference AWD discount code which gives me a rate somewhat below any other of my AWD discount rates. The trouble is that this AWD is "not compatible" with my Wizard number.

Not able to work out the conflict online, I go ahead and make the reservation with the intention of calling up Avis to add the Wizard number. They can't make it work either. I get passed around and end up at the Wizard Desk who are able to add on my Wizard number. All's well and good until I go online to check the reservation, and yes, the Wizard number is now in there, but the discount AWD has been replaced and the rate has gone from about $50/day to $230.

I don't care about an upgrade (as in this case I would prefer a smaller car), but I would like to have the Preferred Service, though it increasingly appears that I'll be finding myself lining up at the counter.