Usually, this indicates that there is an error with your payment method, and it's best to contact your bank (or other financial institution) by calling the 800 number on the back of your card.
Also, you may wish to confirm your payment settings with Express 1 by following the steps below:
Head to your Account Settings (the wrench icon in the upper right).
Next, select Shipping and then Carriers & Fulfillment from the sidebar on the left.
Click Edit for Express 1.
Then, just click on the link to go to your Express1 account management page.