Bernard has figured it out, and I think his suggestion to go to "File," and "Export MIDI-format 0 file" should work.For the record, Sorcha sent me the midi, which played just fine when I double clicked on it.
When I tried to drop it on mid2txt, I got the error message.
I opened it with Cakewalk and saved it as a MIDI format 0 file.
I tried dragging and dropping that one onto mid2txt, and it worked fine.
Now I have to listen to Bernard's tune.