Search all income forms for longish names. TT support claims 15 characters is the max, which seems stupid. I eventually found a 20 character name on a K1 that when shortened allowed it to file. It is very frustrating that the diagnostic can't take you to the right place to fix it and that support seems to know less about the issue than the forum. This has been a multiyear problem for the Iowa return that never seems to be addressed.