your purchase could not be completed
I have a problem
When I wanted to buy from inside one of the games I figured this message
your purchase could not be completed
contact itunes store support to complete this transaction
iPhone 5, iOS 6.1.2
Evidently there are two Apple IDs that have been used as sometime or another on your iPhone. I get the same message on my iPad. Luckly I've recorded my two IDs.