I tried several times to purchase Fallout yesterday, to no avail. Each attempt came up with an error processing the request. After many tries I just gave up.
Today I tried to make another purchase at a convenience store, but my credit card was declined. I called the company and was told that because the server is hosted "overseas" (to my knowledge it's hosted in Canada) They blocked the payment, believing it to be fraud.

It might be that you are a teenager and have a "teen" credit card? Like i live in Sweden and we have just one like that. it cant be used over the internet. (Its free for teenagers and students and so on, but limited to "off-the-net-stores" only and everywhere ofcourse).

My bank did this to me when I moved to Japan. The bank said they noticed transactions from a different location them the 'norm'. I had to go to the bank and "authorize" each transaction. Now they have some phone system that a computer calls me if it notices transactions outside of my registered location.

i had this same problem using firefox. I switched to ie and the order went through.
maybe its a browser based issue? For me, it certainly wasn't an issue with the bank.

I've had similar problems with my VISA. Every so often I come across a web site that glitchs and won't process the card. Of course, I think I did something wrong so I try it again. At the bank, they have fancy (but stupid) fraud detection software. If a charge is repeated multiple times in a short time span, the computer automatically cuts out my account until I call the bank to clear it. Of course I never know the card has been cut off until I try to use it and get denied. Blizzard Entertainment's billing system, flat out, refuses to process my card. After having my account frozen twice after going to their web site, I have swore to never try and buy anything from them again.

Within two minutes of my first purchase at GOG, I had VISA calling me saying my account had been flagged for fraud. The reason being, I had made a few small purchases recently. They saw some more for $5.99 each, and thought it was abnormal behavior for me (and it is really). They locked my card till I verified myself over the phone and said that they were legitimate purchases made by myself, and not another person.
At first it scared me till they explained the reason. This may be similar to what is happening to you, although a card company should call if you have been flagged. I would suggest calling them to see what is up regarding the fraud.

I really hope the GoG team is doing something about this. I'm not even able to purchase any games; I had to convince my friend to let me use his coupon code.