I can't download or update my existing apps because my credit card on file has a zero balance. Everything I'm trying to do is free though. Any suggestions as to how to correct this problem???

Hey Melissavencill,

Thanks for the question. It sounds like your issue stems from the insufficient funds on the credit card. Because the iTunes Store requires active payment information simply adding a separate card, or an iTunes Gift Card may resolve your issue.

The iTunes Store will place a minimal authorization hold on your credit card each time that you update your account information (equal to around 1 USD or your local currency equivalent). The authorization hold isn't a charge. The authorization hold is placed on your credit card to make sure that the information provided matches the information on file with your financial institution. The authorization hold won't appear in your iTunes Store purchase history.

iTunes Store: Changing your payment information

http://support.apple.com/kb/HT1918

Thanks,

Matt M.