For online purchases, the credit card processors require an added layer of security to prevent fraud.  The address that is entered at checkout must match the address that the card issuing bank has on file.  The address might include abbreviations such as DR for Drive or VA for Virginia.  Many times we see situations where a user changes their billing address online, but the original billing address is still associated with the card.  Check with your bank to verify the correct billing address for the card.