I've now had 2 bad experiences with both Hotwire and Travelocity. Although not really rental car related, they still screwed stuff up with hidden charges and surpises after the fact. I can't say for sure if it was really their fault but I've given up on them.
Just for giggles did you try going to the actual company site for the rental car company? 99% of the time that comes out the same for me anyway and you have fewer problems.