Tax returns prepared before tax year 2011
You can only transfer information from the previous tax year; you can't skip years. For example, you can't transfer 2009 or 2010 tax information into TurboTax 2012.
Tax returns in PDF format (TurboTax Online)
It is not possible to transfer from a PDF file in TurboTax Online. On the other hand, TurboTax CD/Download software supports PDF file transfer. More info
Information from a different main form
You cannot, for example, transfer data from a corporate (Form 1120) return into a partnership (Form 1065) or individual (Form 1040) return. You can, however, transfer data between 1040, 1040A, and 1040EZ returns.
ProSeries or Lacerte tax preparation software
TurboTax cannot transfer information from ProSeries or Lacerte programs; however, these programs will accept TurboTax data transferred to them.
Multiple returns
You can only transfer information from a single tax return. For example, if a newly-married couple filed as individuals last year, but plan to file a joint return this year, they will only be able to transfer one spouse's return into this year's joint return.
TurboTax Online Free Edition
Tax files created in TurboTax CD/Download software versions cannot be uploaded to TurboTax Online Free Edition.
TurboTax Freedom Edition
TurboTax doesn't allow you to transfer to or from Freedom Edition.