I had a similar issue. I made a project yesterday. Went to open it today and nothing was there. Just an empty project file.
I solved it this way with AppleCare's help:
QUIT iMovie First. Then...
1- Go to: Home > Movies > Right Click and 'Show Packet Contents' for "imovie library.imovielibrary"
2- Locate the project you want to open that has gone missing.
3- Delete any special characters (&, $, #, ?, etc) both in that folder, and in the folder within that folder of the same name.
4- Drag the .flexolibrary file to your desktop
5- Go back to: Home > Movies > and double click on "imovie library.imovielibrary"
6- iMove should open and your project should be there.
AppleCare states that special characters cause the file to become 'lost' to the library.
By changing that and then throwing out the .flexolibary file, AND THEN reopening it, you are forcing iMovie to re-look at your project files.
Hope that helps.
This just happened to my daughter on a school project that is due tomorrow that she had spent hours working on. After reading this forum she went to bed despondent. As a desperate mom with no knowledge of Macs I stumbled on something very simple that I hope will help some others. Her project was on her desktop - when we right clicked and said "Get info" it showed it was full size 85 MB; double clicking the icon caused iMovie to open but the project was not in her project library and we could not drag it there.
When we opened the" iMovie Projects" folder (found that by opening Finder and then from the top of the screen choosing GO -> Home -> Movies -> iMovie Projects) there was seeminglying the same icon with the same project name; but, "Get Info" revealed that this file was only a few KB's - not the full 85 MB's. So, we deleted the very small file, drug the full sized file from the desktop into the iMovie Projects folder, double clicked it and it worked perfectly!
I hope that this helps someone else! I'm going to bed now - sleep deprived but my daughter's project is saved!