I've got a Youtube video I pulled in Captivate 2019 update 2. I added a quiz question then duplicated
it 8x for Multiple choice questions with Results slide. When I got to "insert overlay" on the video
I get an error message saying "There must be slides in the project that can be used for overlay"
Why won't it accept my set of Quiz questions for that?
Scored question slides are not eligible for use as overlay slides. You can use regular slides and Knowledge Check questions as overlays.
Only KC slides and content slides can be used as overlay slides. If you need scored slides, which do not have to be reported, there may be a workaround. For reporting you'll need to have quiz slides outside of the interactive video.
BTW it is not a good practice to duplicate quiz slides, can lead to unexpected problems. Set up the quizzing master slides before inserting quiz slides. Much better practice.