Thank you for contacting iTunes Music Store Customer Service.
You may need to refresh your account information. Please follow the steps outlined below in order to refresh your account information.
First login to <http://myinfo.apple.com> with the account that you are using on the Music Store. Then modify your billing information and hit the save button. A simple modification would be to add a single blank space to the end of your address, or you can complete the change of credit card information from this page as well.
Once your myinfo page has been saved, please log back into iTunes and try to make a purchase. You should receive an error message stating that your billing information has changed, click review and you can either modify the information, or if you've already made the modifications on the myinfo page, simply hit save.
This should resolve the issue with your account and allow you to continue using your Music Store account. Should you experience any further issues with your account, please reply directly to this email including specific information regarding any error messages that you may receive.
Find answers to many technical questions in the Help menu or at the iTunes Music Store Support website:
<http://www.info.apple.com/usen/musicstore>