Tom,
I had the same thing happen this year. You can still file electronically as usual, you just need to print out the Forms 8949/8453 separately and mail them in.
It would be nice if TT let you know ahead of time what was going on, but it doesn't.
It appears that mine was triggered by either 1) some Robin Hood investment transactions that were too numerous to fit on Schedule D or 2) a few sales of scrap gold, thus triggering the Form 8949 where "additional info" is entered.
It's no big deal, just additional info that won't fit on the Schedule D for capital gain.
Good luck!
Herb
