ITunes :: Error On Movie Category?

I have movies that i have downloaded, ive converted them into m4v. I've tried to move these to a new folder called music video. when I do this itunes freezes then errors so I have to force quit. When I restart  it sorta looks like the video is still there but a generic picture is there and the video wont play, its like its there but not at the same time. This has happened about 6 times now on 3 different shows. I delete and recopy to itunes, try again and it does this all over again. Now I just copied it in again and Im leaving it there till theres a solution, at least here it works, but i would like to organize more. I never had this problem before and to honest, im not eally sure when it start, but very recently.FYI, this is Itunes 10?