I had a similar thing just recently. I was sitting in a hackerspace trying to book a hotel. It wasn't possible there because they wanted a credit card (just as safety if I don't show up, I was going to pay in the hotel anyway).

Since I don't have a credit card, I IM'd a friend if I could use his credit card for the booking. I went over to his place, and when I did the booking process at his home, suddenly I could book without a credit card.

My hypothesis is that the hotel website didn't trust me in the hackerspace since I was connecting to them over a VPN.