Logic: bouncing project results in empty audio file

I'm using Logic Pro X on an iMac (late 2013), 3.4 GHz Intel Core i5, 8 GB 1600 MHz DDR3, OS: Sierra 10.12.6.

Ever time I try to bounce a certain project, it "bounces" it, but the result is a 4 kilobyte audio file (MP3)-- which, obviously, is ridiculously too small. The project is 11 minutes long, all internal software instruments. Of course, I've tried the usual-- set the start and end times correctly, selected all tracks, made sure. All channels are sending to the stereo out.... tried it in real time and off line, etc., etc., etc. Nothing works. The WAV and MP3 tracks appear, but when I double click on them to open them, iTunes will open, and then kind of act like it's about to load the new track, but it never gets loaded and nothing happens. Like I said, it's a miniscule size track-- 4kilobytes. And it doesn't even matter how much of the project I select to bounce-- always ends up as a 4kb file.

This was a project from a previous version of Logic, so that's possibly where to look for the answer, but I don't know how. I've done this before without a problem. Please let me know if you have any ideas-- thank you.