Please help!!!

Hi Guys

I was wondering if someone could help because I have a big problem when trying to export a movie that I have made in IMovie to my desktop (file).

I have created a movie which is 21 minutes long which consists of pictures and video clips. When I try to export it onto my computer everything looks fine, I get the blue swirly circle (progress bar) at the top of my screen which slowly fills however when it finishes processing which seems to take forever the video is cut in length from 21 mins to 4-7 minutes. Each time I try at different resolutions e.g SD or large it only seems to do part of the video and it copies a random video length, the longest I have got was 7 minutes and 1 second of the 21 minutes.

Has anyone encountered the same issue or know why its happening?

Please help!!

Many thanks

Luke