Hi, Community User,
The first thing is to update your iMovie 10.1.4 to the highest version that your Mojave operating system will run. To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You
will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash and return it to the Applications folder. See if that helps.
If not, Make a duplicate of one of your clips and convert it to H.264, Mp4/AAC with the free download, Handbrake. Do that even if the codec already is indicated to be Mp4/AAC. Re-rendering often cures the issue.
You can get Handbrake here:
https://handbrake.fr/
A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to complete. Then save and import the converted clip into iMovie. Now see if you can share out the converted clip in a new project.
If still no luck, try 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. Now see if you can share out.
If still no success, then read on. The CompressorKit error is very pesky and has been reported frequently on this forum of late. It seems to be related to an iTunes update that implants a 64 bit architecture into the system library. Thus, some people have solved this by upgrading to Catalina, that is a 64 bit operating system. However, that would render inoperable any legacy 32 bit programs that you may have on your Mac, and also some legacy media would not play in iMovie and would need to be
converted.
Sometimes booting up in Safe Mode (see Finder menu for instructions) and
immediately shutting down and rebooting in normal mode helps.
Recently there has been a breakthrough on this issue, discovered by nicocaro, who posted a solution on this forum. Below is a link to the thread where he describes how to solve the problem by removing a 64bit architecture from an iTunes update. Other posters have successfully tried the solution.
Here's the link to nicocaro's solution:
https://discussions.apple.com/thread/251266351
And here as well:
https://discussions.apple.com/thread/251352619
After doing the above your iPhone likely will not sync, although iMovie will work. To get your iPhone to sync again, see this link that solves that issue:
https://discussions.apple.com/thread/251916124?answerId=253660165022&login=true
Here's another link, though older, that describes what others have tried with the Compressor Kit Error:
https://discussions.apple.com/thread/8265338
There may be some proposed solutions in the above link that will work for you.
All else failing, try calling Apple Support. The techs there are very savvy and also have the capability of remotely accessing your computer. Click on the Contact Support item in the upper right hand corner of this screen and navigate to a place where you can provide your telephone number so that Apple Support can call you back. I think that the file path is Contact Support/Mac
OS/Applications/iMovie. Good luck with this. If you have time, post back with your results, as it may assist others who have this perplexing issue, and will contribute to our data base.
-- Rich