Mike9241, thank you for your answer. It was indeed the case that a summary total, with code M was entered for one line on 8949. However, it was not a summary - but a single transaction, which was marked incorrectly as a summary. When I corrected it, TT stated that everything is complete and I do not need to file additional information. Unfortunately, I had already filed (I wish TT had said that I need to file 8453 BEFORE I transmitted my e-file, and then I could have corrected this). Unfortunately, the only option to correct this now would be to file an amended return. Should I do this or just mail in the 8453, along with the details of this one trade (and perhaps an explanation that it was indicated incorrectly as a summary)?
