This issue is happening to me as well and I have noted it on a similar topic about this as well. Their setup is confusing if not messed up and may be in need of reworking. It worked for me only once before it refuses to do so. It may be because the billing address on the account is not the same as my billing address on the card since it compares that information. For example, the PSN seems to have a fit when entering a PO Box for a billing address when inserting the credit card and says that the card is invalid or some sort.
I just bought 6 games off the damn thing and the same day tried one more and have been getting the same error code for 2 days now they said there doing maintnence now thats done and instead of an error code it just says cant add funds to wallet even tried qrocity or whatever it is and it tells me my card info isnt valid but i knw for a fact it is and i knw for a fact theres plenty of money on it so wtf is the problem here eh pissing me offffffff how can i buy 6 games in one day then cant a couple hours later and havent been able to for 3 days now makes no sence wutever screw playstation time for my pc or buy a new 360