Error: RequestFrameAt returned: 3 for absolute frame: 796

The message means that there is corruption at frame No. 796 that is blocking the export. Usually it is a black frame. Expand out your timeline with the slider at the upper right of the timeline. Scroll around the area of frame No. 796, looking for black frames, white flashes, artifacts, and any other thing that looks like corruption. Cut out any that you find and then try exporting again.

To find frame No. 796, divide your project's frame rate into 796 and that will give your the time point in the timeline where frame No. 796 occurs. So, for example, if your project is 30 frames per second, divide 30 into 796 = 23.57 seconds = 0.44 minutes. Therefore in this example the corruption in the area of frame No. 796 occurs at less than half a second into the video at the 23.57 time point. Be sure to scroll all around the area.

-- Rich

If the black frame is showing up in replacement transitions and with different transitions, then the problem is with the clips on either side. Try trimming back the clips on either side of the transition and see if that solves it.

Also, to cover the bases, some people who experienced this issue cured it by deleting preferences. To delete preferences, open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

To rule out that the black frame problem might be confined to just this one project, try putting your media into a newly created project and see if that cures it. You only need to put the two clips at issue into a new project and see if you can add a transition and successfully share it out.

-- Rich

"half a second into the video" -- I meant to say "half a minute into the video". Sorry for the typo.

-- Rich

Great! Looks like it’s solved. 😊

— Rich