Error 50 is a rendering error that indicates corruption somewhere in the project Sometimes it can be difficult to locate the corrupt frames. You've taken the correct approach in trying to isolate the problem. It may not be a clip that is corrupt, but perhaps a corrupt font in a title. Working with a duplicate of your original movie, try eliminating all the titles and then share out. See what happens.
Deleting preferences can sometimes resolve share out problems. Try opening iMovie while holding down the Option and Command keys and selecting 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.
Another thing you can try is to copy your media into a newly created project and see if that cures the problem. To do
that, do an Edit/Select All, Edit/Copy, of the media in your project and then Edit/Paste it into the newly created project. Also try creating a new project and putting in different media and sharing out.
Try creating a new library and copying your project into it, and then sharing out.
Is there anything odd about the formats or frame rates of the clips being used?
-- Rich
