A couple pages earlier in this thread, someone showed this was happening with their reload attempts and they had to call Discover to get their account unlocked. It was the same message ("debit not available") but I guess there are different reasons why it might appear. In my case, it seems Walmart wasn't even attempting to charge the prepaid card, which makes me think that type of card might be blocked by some Walmart locations but not others. I'll try to narrow it down next week!