...and if it's the youtube tags you are using then make sure to only copy/past was is after "watch?v=" from the link address.[video=youtube;gr4IxMgHdDY]http://www.youtube.com/watch?v=gr4IxMgHdDY[/video]
It can be either on "Insert Video" or in the Youtube tags at the side of Spoiler (Go Advanced)