There have been a few occasions recently where You Tube embedding links appear not to be working.
There is no longer a requirement to quote the full link - for instance this link
youtube.com/watch?v=g0-xnaRSL6g&feature=player_embedded [http://www. removed to show full link]
will only now show as a white square.
The only piece of the link now required for embedding is the bit after the '=' sign and before '&' sign
EG: g0-xnaRSL6g as shown in red above [enclosed by the youtube bracketing] will give you.....
Please see this post in Forum Support for more background
http://www.iconicaircraft.co.uk/forum/viewtopic.php?f=5&t=3035&p=133470#p133470
Edit - small change to grammar - sorry ... SF