PLEASE NOTE: I don't work for Apple... I'm just a fan and I just want to share an idea! Few days back, I had the same problem trying to purchase some Apps with my account which I had been doing for a long time. So, once I hit 'buy' this annoying "Please contact iTunes Support to complete this transaction" pops! I found this forum while looking for solution which almost discouraged me form contacting iTunes Support... well, I gave it a try anyway. Here is the first message I received immediately:
Dear customer,
This is an automated reply, but an iTunes Store representative will review your request and send you a personal response, most likely within 48 hours.
While you are waiting, you may wish to review this article:
iTunes Store: Best practices for protecting the security of your account
http://support.apple.com/kb/ht4156
Please do not reply to this email message. It was sent from an address that cannot accept incoming email.
Thank you for your patience.
Sincerely,
iTunes Store Customer Support.
Folowing this 20 minutes later:
Dear Emmanuel,
I understand you are getting a message to contact iTunes support when trying to purchase apps. I can certainly appreciate your concern. My name is Susan and I am happy to look into this for you today.
I am pleased to tell you that I had your account investigated and the necessary adjustments have been made to your account which should allow you to purchase from the iTunes store again. However, you will need to wait 24 hours since your last attempt and then you can try again.
If you are then still unable to purchase, be sure to let me know.
Thank you Emmanuel for being a valued iTunes Store customer and have a great day!
Sincerely,
Susan
iTunes Store Customer Support.
After like a day of not responding to them/her, here is what received:
Hello again,
I wanted to send a quick note to see if you are still experiencing any difficulties with the iTunes Store. Resolving your issue is important to me, so please don't hesitate to reply if you need any further assistance.
Sincerely,
Susan.
All I'm suggesting is just for you to contact iTunes Support with this link:
http://www.apple.com/support/itunes/contact.html?form=account&topic=iTunes%20Sto re%20Account%20and%20Billing&subtopic=Account%20Security
...and make sure you fill everything there right. Hope this helps because after 24 hours, I started making purchases just like before.