First, please make sure that you have purchased the right product. The codes for TurboTax Online will not work with TurboTax CD/Download & vice-versa.
Second, if you bought TurboTax at a retailer (Costco, Walmart, Staples, etc…), please make sure that you are using the code that came in the package. It may be on a slip of paper or on a scratch-off card. It is not on the outside of the box or on your receipt.