iMovie 11 freezeing Constantly?

I have 20-30 3-8 minute movies in my project file. I'm trying to transfer some to iTune and then to my iPad. I try to scroll down to the one I want and the little ball spins forever. I often have to force quit and start over but it just starts all over again. I can get one move shared to itune but rarely can do two without restarting. What is wrong?

I transfered the iMove files I least need on this drive to and external drive but I am afaid to deleate the movies. Will the exported files reimport to iMovie as they are so I can edit them if I choose?

I have a 500 Gb HD with 100 free.

Thanks Tina