Well, since we're adding new options I'm gonna share what's been working for me perfectly ever since I started using it.
1. uninstall DownloadHelper. it sucks.
2. install either Easy YouTube Video Downloader or Flash Video Downloader
3. for surther conversion uninstall Any Video Converter (if u have it installed on your computer) and install iWisoft Free Video Converter. I'm in love with this converter.