If you change it back to the basic editor you will see what has happened to the link:
http[color=#666600]:[/color][color=#880000]//www.youtube.com/watch?v=hvoD7ehZPcM[/color]In order for it to work, I think the colour tags need to be deleted.
As Tacymist said, it would be easier for him to just go on Youtube and copy the video link himself from the address bar though. Paste it in a post, and click "preview". It should be working.