When I noticed you had problems posting a link to a YouTube video, I thought I would tell you all what I do when I have the same problem (hope I am not teaching people to suck eggs).
From time to time my iMac decides that it will not let me use the "share link" feature in YouTube to post in this forum.
What I do is:
In YouTube, click the 'Share' button.
Then click on the 'Embed' button.
This will show a box with some text highlighted in blue in my case (see below example). This text can be copied and then placed into your GaGa post using the 'HTML' icon.
Example: " <iframe width="420" height="315" src="http://www.youtube.com/embed/v5N46p2aU68" frameborder="0" allowfullscreen></iframe> "
If you have as in my case written some text before you click on the HTML icon, you will need to scroll to the end of the existing text before pasting.
I have used this method to post the excellent song by OMD below.
Hope this is of help to some of you.