Something is terribly wrong with Nokia's system in which they charge your card and their customer service. This same problem happened to me. I tried to place my order on NokiaUSA this weekend since the sale was going on and they have the phone in stock. At the last step I get an authorization error even though all of the information is correct. I tried 1 more time and it still did not work. I called them to place an order over the phone after waiting 20 minutes on hold, the same thing happened and it was not authorized.
When I called my credit card company, they said that 3 temporary charges of $613 were charged onto my card, but Nokia is saying that it did not go through. They told me to wait a day and try again. Today, I tried again this morning and I get the same error so I called Nokia and was on hold for 30 minutes this time. They tried to place the order and the same error occurred. I called my credit card company and they said over $3000 in temporary charges were on my account made by Nokia.
The credit card service rep and I 3-way called Nokia only to wait another 30 minutes on hold. The rep at Nokia said "wait 2-3 minutes while I check your file." He returned 20 minutes later to be yelled at by my credit card rep about terrible customer service. The Nokia rep said there was nothing he could do and that I would have to wait at least 3-5 business days before attempting to order again and that I would have to pay full price in 3-5 business days since the sale would be over. 2 Reps from Nokia also said that they would "call me back in an hour" to resolve the problem and try to get my order through, but of course there were no callbacks.

My credit card company was able to cancel all of Nokia's $3000+ dollars in temporary charges.

In the end, Nokia has VERY terrible customer service. Their online shopping system is flawed (they couldn't even get their prices right for a day let alone charge me to buy a phone). They can't do a simple purchase because of their servers. They couldn't even take a fax giving authorization from my credit card company. They can only go through their online system to take orders. They suck.

I was about to completely give up on the N900, but I'm with T-Mobile and their 3G capable phones are terrible. The N900 does have a lot of flaws, but it seems to have potential and it does use T-Mobile 3G. The thing I'm worried about is the way Nokia handles things. I hope this doesn't carry over into support for the N900.

Luckily I found a seller on eBay with 1800 feedback and 10 N900's posted at $750 or best offer. I made a reasonable offer and he is shipping it Monday.

Hope you're able to solve your problem too.