Update - I've successfully e-filed now. To do this I had to go back to the "forms view", find the federal 1065, and check the box that says, in effect, "even though I'm not required to file a Schedule L, I will do it anyway".
I noticed when I did this that it immediately added a few "errors" to the schedule L to the effect that it was out of balance. Behind the scenes, TT had not properly set the partner cash contribution shares so it looked as if the partners had just contributed them this year instead of all those years ago. It also had no cash balance reflecting the partner's cash shares. I fixed those entries (adding a "beginning of year", deleting this year's contributions, and setting cash on hand to reflect).
Then voila! e-file worked.
