My iMovie '09 will not let me "share" or "export" videos! Please help!

S.O.S !

My iMovie '09 on my mac osx will not let me export my edited videos.

When I try a message pops up and says "The project could not be prepared for publishing because an error occurred. (-50)"

I have searched around and I've found that the most common answer to this problem is that there is not enough space on the hard drive, i have 530 GBs of free space so surely this can't be the problem.

Another answer i've seen blames the problem on Time Mashine, I've tried turning T.M off and unplugging my external hard drive. This too doesn't help.

I discovered that there was a problem with my hard disk but started up my computer with the install disc and successfully repaired it. Also this did not solve anything.

How can i solve this problem? Or atleast get around it -I tried moving the project file to my flatmate's mac to try on her iMovie. But her computer is brand new and it didn't work.

Anyway, i hope someone out there can help me with this.

Thanks