iMovie 08 v 7.1.1 - Can't export - Error -108 - Help Please!

Please can anyone help?

I'm a new Mac user and have just imported and edited my first iMovie. I tried to export it (assuming I could then burn it to a DVD?) but never got that far.

I'm attempting to export it as a 'large movie' to Finder.

I get an error telling me it has been 'unable to prepare the movie for publishing due to an error (error code -108)'

Please has anyone got any ideas if I'm doing something wrong?

Thanks!

D