Error message when buying songs When to do when you get this message while you were purchasing an album?

How are you supposed to contact support? Is there an email address for this? A specific phone number?

Please contact iTunes support to complete this transaction.
Here's how to find the way to contact Apple:

Go to apple.com and click Support.
On the Browse Support section on the left, click iTunes.
Click Music Purchases in the Get Customer Service list that appears in the middle.
Click Music Purchases in the sublist that appears.
Click the Email Us button that appears.

Here's a direct link to the form to fill out to contact them for a iTunes Store music purchase issue.