I have just upgraded from Vista to windows 7.  I have previously made many DVD's on MovieMaker in Vista.  I have now created a new project including photos , video and music but cannot save the movie to burn a DVD.  The project is approx.20 mins long but when I try to save it I get a message that there is insufficient space.  I have the project on an external,hard drive with a huge amount of space available on it and I still get the same message.  I believe I have all the latest Windows updates and the relevant DVD maker programme.  Any ideas?  Please keep suggestions in plain English as most computer-speak goes over my head!