Hi, praemarc,
Unfortunately, there is no "debug mode" in which to run the export to locate corrupt clips.
Some solutions that have worked for others are:
1. Create a duplicate of the project and export that.
2. Reposition titles. (Also can try changing the fonts in titles in case of a corrupted font.)
3. Convert your clips to .mov or Mp4 -- no mixed formats among clips.
4. At the point where the movie stops rendering, find that point in the project and remove some frames before and after.
5. Copy and paste the project media into a new project.
6. Update both operating system and iMovie version to current.
7.Copy the project into a new library and share it from there.
Titles and fonts can be a source of render failures. Third party fonts have also been known to cause problems. You might want to do a font validation to see if there are problems with any fonts that you may be using in the project. To do that, go to your Applications folder and open the Font Book app. In Font Book, select all the fonts by highlighting them as a group. Then do a File/Validate Fonts. Any corrupted fonts will be identified. Do an Edit/Disable Font on any bad ones that you find. Further, sometimes duplicate fonts that are not corrupted can cause problems. Do an Edit/Look for Enabled Duplicates and disable or remove any duplicates that you find.
Sorry you are having this trouble. Nothing to do but keep experimenting until you can pinpoint the point of corruption.
-- Rich
