Error -50 while trying to export my project

Good evening,

I built a 1h18 project.

Then, I chose to delete not used plans from the associated event.

As my project is too big to share it on my MobileMe gallery, I would like, either to share it in a smaller format, or to export it or to build a DVD with iDVD.

Unfortunately, each time I try to proceed so, iMovie answer me with a pretty -50 error message.

I don't understand why, as I can watch my project without nay problem.

Could anybody help, please?

Thx

Claude