Problem with imovie - lost project

I have just been handed back a MacBook on which a student made a short film which they saved on the desktop, i was asked to add some music, when I opened the project it is empty. The class teacher assures me she watched it, she also copied it to a memory stick and to her own macbook, each project is empty.
I have tried importing the TimelineMovie.mov from the Cache folder but I just get "cannot import file unknown error"
Any ideas where it may have gone anyone?