Why is my account unavailable??

This has happened before, but this morning I cannot download a FREE app, so I go to the store settings both in iTunes on my Mac and on my iPad, and it tells me I need to put a security code for my credit card. Every time I put it in, it says that the account has changed while I was editing it and cannot be saved. I simply won't save my security code, although it was saved before...It's just weird and it's making me mad.

 

yeah ok, maybe that would work for THIS app, but I'm really looking for more of a permanent solution to this recurring problem. Dont really feel like deleting my card either. It hasn't done it in a while, but it has definitely had an issue saving my 3 digit security code before. And no, there is nothing wrong with my card...