This is from Visa's website
Quote:
Can I use my Visa Gift card for online or phone purchases?
Yes. However, to make an online or phone purchase, you will need to register your card. You can do this by either calling the issuer, or by visiting their web site.
When you make an online or phone purchase, the name, address, and phone number you use will need to be exactly the same as the information you provided when registering your card. If the information is different, the transaction may be declined.
You can verify or update your information by visiting the card provider's web site, or by contacting them using the toll-free number provided in your card documentation.
Can I use my Visa Gift card outside of the United States?
If your gift card states Valid only in the United States on the front, your issuer has issued a Domestic Use Only card. Although your gift card will not be accepted at locations outside of the United States, it's welcome at millions of locations within the U.S. where Visa Debit cards are accepted.
Squirrel, did you register the card online with the same billing address or try to use it without registering?