Rich, first of all thank you so much for your immediate reply. Reading your reply I gave me back the will to live.
The solution could well have been a lack of space on my hard drive. I had 35 available GB, and to copy the movie to my desktop I needed less than 12GB. After you replied, I figured 35 still wasn’t enough space, so I used Clean my Mac to delete Theater. Theater always seemed a little redundant anyway. Doing that freed up over 50 GB, after which I was able to create an MP4 on my desktop, and from there I’ll be able to burn it to a DVD.
I still couldn’t figure out why YouTube was kicking me out. Then I realized that in utilities I have my battery set to power down after three hours. I changed that from three hours to “never“ and I also changed my screensaver not to run, just in case. I’m halfway through the upload to my YouTube account and fully expect it to work this time.
Thanks a million!!