If you are having issues updating your previous iMovie projects, you may find the following article helpful:
If you look into your iMovie projects and events folder you will find that iMovie version10 (it is version 10, iMovie '11 = imove v.9) has added an empty file named something like "updated to imovie ....." in order that it doesn't update the same projects twice.
If you trash this folder in both the projects and events folders, iMovie 10 will be able to update them. Of course you need to temporarily hide the projects and events which you have already successfully updated.
You probably have a single project or event which is causing the problem so I would advise updating just one project at a time. You will get a new library for each in iMovie 10 but you can sort this out afterwards.