You need to spend some money on credits to be able to sell, you won't be able to sell if you buy a deck with the credits you have earned in tournaments
You should be able to sell after bying credits from the shop!
Try one of these:
1. Log out and in again or,
2. If it doesn't help, then buy something from the shop (that's why you bought credits right?!? :) )
Hopefully it helps... :)
No, if it's credits you got from participating in tournaments, it will not work.
Basic rule of thumb - If somewhere along the line you/someone else did NOT spend real life money (credit card, phone, paypal whatever) to get the credits, it ain't gonna work.