"Unable to Purchase" music that is already purchased

I have an iPad 1 and an iPhone 4S, both running iOS 5.1.

When I attempt to play music on the iPad that is NOT already downloaded to the device, I get a message:

Unable to Purchase

"Virtuoso" and 20 other items could not be purchased at this time. Please try again later."

OK

I click "OK" and everything works. The music downloads and plays just fine. Once downloaded to the iPad, it plays normally.

Here's the thing: "Virtuoso" is an album I purchased from the iTunes store weeks ago on my iPad. I have the files, I have even made a CD of it on my Mac. For some reason the iPad keeps trying to "purchase" it (and 20 other files as well).

This message does not appear on the iPhone, it just works.

I have tried resetting settings and restoring the iPad (no change), turning iTunes Match on and off, and logging in and out of the Store. No joy.

Any ideas before I just contact Apple? Thanks, all.