There are some uncommon situations where additional documentation must be mailed to the IRS with Form 8453. Please see the link below (which may download a PDF file) for situations this may apply. TurboTax would have instructed you, if this was your situation.
Please click on the link below to retrieve Form 8453. If you save this form on your computer and open it with Adobe Reader you will be able to type into the form:
https://www.irs.gov/pub/irs-pdf/f8453.pdf