I am trying to get the 14 day trial and it keeps popping an error. I even tried paying for a month and that failed as well. I've tried this from my phone as well as my pc. What is the deal???
Try Zune.net - It works there.
If you have XBOX, it might be worth a shot.
Also, if your card is recently expiring, it will kick issues. If you open a ticket with Zune support, they will call you back and will get it sorted in less than 10 minutes (if that!)