I was unable to enter the code on the PS website as well (gave me an error stating "This Prepaid Card cannot be redeemed on a PC"), but when I signed on to my Vita at home and entered it, it worked just fine. Just remember to enter it before it expires on March 31.
Took almost 2 hours from the time I submitted my order, but I finally received my code after contacting customer service via the "Live Chat" at the bottom of the screen with my order #. Normally would be more patient than that, but never had even heard of the site before so I was already a...