Purchase cannot be completed

Most of the people on these forums, including myself, are fellow users - you're not talking to iTunes Support here, we won't know why.

If you are getting a message to contact iTunes Support then you can do so via this link and ask them for help : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

If it's a different problem ... ?