You might have a rogue black clip on a higher video track. In the timeline check to see if it has a scroll bar at the right. If it has, scroll up to view whatever lurks there. Also zoom in so you can check more thoroughly.
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Thanks, but I checked that and there wasn't anything. It rendered OK finally and is now up on my gallery. But I'm worried that it might happen again during some other project....
One possible issue can happen, when one is using a GOP (Group of Pictures) format, like MPEG, and Delete an I-Frame. They are then left with ONLY the difference Frames, until the next I-Frame, which can be 15 - 18 Frames along. This ARTICLE goes into more detail. Editing GOP material can be problematic, because of their structure.
I believe you got it right, Bill! I did have five or six pictures on the same Video 1 timeline field just prior to the clip that rendered black and a transition connecting them. I never realized that might cause a problem, so I didn't mention it in the original post. So that apparently is the cause of the problem.
The clip that rendered black was actually the first fourth of the whole film I was editing. I had cut it from the original to capture a freeze frame to use as the background of a title coming before the clip that rendered black. The 2nd clip I rendered of the same footage also rendered black, as you know, but when I deleted the entire movie track and used the whole movie clip, the rendering was perfect. So the original black clip's length may have also had something to do with the problem.
Thanks a lot!