What are you trying to purchase?
Trying to purchase the Age of Empires Online (free) game with Microsoft Points, either on the web or through the Games for Windows Marketplace client.
What error code or message are you receiving (from the console)?
No console, PC user here. The error does not specify a code, it reads: "Sorry, this transaction cannot be completed at this time, please try later".
Additionally, an unspecified error appears when I attempt to add a new payment method to my account (credit card) but I don't think this is topical.
What region is your account?
What region do you physically connect from?