I've just started having this problem with iMovie v4.01. Running on Mac OS X v10.3.6.
I am working with children making iMovies using still images.
Whenever the kids add a title to their project, if they attempt to edit the title or change it in any way iMovie is unexpectedly quitting, but I am getting no error message.
I have tried trashing the preferences, and removing what I thought were the offending plug-ins (no non-standard ones installed), but neither of these have fixed the problem.
The problem is inconsistent, however each computer (G3 iBooks) has the exact same software configuration as they have all been imaged from the same image.
I have managed to add titles by copying their iMovie project folder onto a G4 iBook, however I haven't tested editing the files on same.
This is getting very frustrating as on our previous image, it worked fine.