If you owe any money, you cannot simply remove your CC details.
You need to add a valid credit card.
It also says that I owe iTunes $17.56. I don't know why I have to owe iTunes money either.
You have to owe it because there was a purchase. That's how sales work.
Whether you actually owe it, depends on if you made the purchase or not.
Check you purchase history. See this -> http://support.apple.com/kb/HT2727
If you did not make a purchase that shows up, report it.