Unable to export from iMovie 10.3.10

Hi,

Sometimes with an upgrade to a new operating system glitches can occur. Maybe an iMovie preference went awry.

The first thing is to make sure that you have updated your iMovie app to the most current version.

If the issue still persists, try deleting/resetting preferences. To delete/reset 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 empty library. Reopen your old library to get back to your projects. Possibly you may need to reboot to set the changes.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project. Now see if you can export. It may help to create a totally new project and then try exporting. Sometimes problems can occur in one project but not another.

If still no luck, you can try rebooting in Safe Mode and, after every thing loads, shut down and reboot in normal mode. That should clear out any conflicts that might have arisen. This link will describe the procedure for booting up in Safe Mode.

Start up your Mac in safe mode - Apple Support

-- Rich