I've been filing with TurboTax for 15 years or so. I rarely have an issue and they've helped me when I needed it. I usually pay through bank debit when I owe.
This year I was following the usual routine, I e filed and okayed the bank debit.
Then, and I almost missed it, there was a screen that said I STILL needed to paper file or my return would not be complete. What? Why? Has this always been the case and I've skated all these years? I've never paper filed when I efiled and paid electronically?
It could be that your return has a situation where you are required to mail certain paperwork to the IRS to go with your return. Some common situations where this happens is paperwork for certain charitable contributions or a copy of your Form 1099-B showing stock transactions if you entered only summary information in the return. If you electronically filed, you would not be mailing your entire return because it has already been sent.
Go back into your return and take a closer look at the information stating that you need to send something by mail. You can see these instructions on the cover page of your return if you print/preview the complete copy of your return. The cover page will tell you what you need to mail and where to send it.
Also, take a look at the following TurboTax help article for more information: