Maybe your tax liability is already Zero? Certain credits are refundable or partially refundable (like the Earned income credit or American Opportunity Credit) while others are non refundable and can only help to reduce your liability to zero. This credit is a non refundable credit and thus can only be applied to your tax liability and not beyond that. If you have no tax liability for the credit to be applied against, then TurboTax would say your personal portion is zero and the IRS instructions say to not file the form. Here is an excerpt from the IRS instructions for form 8911....."If you can’t use part of the personal portion of the credit because of the tax liability limit, the unused credit is lost. The unused personal portion of the credit can’t be carried back or forward to other tax years."
