I've had problems also. Recently, I was on the Avis site and had problems, so I sent an e-mail to them. I received a reply that said they WERE having problems but were fixed now. I doubt that they were fixed in the 5 minutes that it took me to send the e-mail after leaving their website.

BTW, I think National Car Rental has the worst website I've ever come across, even before their recent troubles. Talk about clunky!