Help with purchase on the blizzard store...

Today i bought a pre-paid master card so i could buy something on the blizzard store, i put in my information and when i click for it to go through and purchase it it gave me the message "There has been an error processing your request", I'm wondering if it takes time for pre-paid cards to work after you purchase them? This one said it becomes activated as soon as the cashier swipes it through so I figured that would mean i could purchase things with it right away.