This usually happens when you are checking out if you don't have enough funds to cover the cost of the invoice being generated. Our hosting plans are typically rated per month but are billed for the full year.
If you are sure you have enough funds available the bank may have flagged the transaction as being possible fraud. You would need to contact the bank to remove the hold from the credit card or find out why this is being declined. If you have already talked to the bank and they said there are no issues with this credit card, please use a different credit card. Unfortunately there are times when the charges are declined and we have no further information.
Billing can assist you with questions like this, and are available Monday through Friday from 8am - 5pm MST.