E-File is not available because your tax return includes a tax situation that can't be e-filed. Make sure to mail your return by your state's due date.

I received the above message while filing my MA state taxes after using TurboTax to file an extension in April. I have done this exact process for a few years and never had to mail my state return. Is there anyway I can find out what form or tax situation I have so I can resolve it?

If the software can determine that I cant Efile, why cant it tell me the reason why?