I can't watch the videos that i download from youtube on itunes, HELPPPPPPP

I can't watch the videos that i download from youtube on itunes. Did anyone have this problem before? HOw can i fix it? This problem just occured recently. It worked just fine before. It happened until i upgrade both youtube downloader and Itunes. I tried to re-download both youtube downloader and Itunes but the problem is still there...PLEASE I NEED SOMEBODY'S HELPPP PLEASE HELP MEEE