At present it seems that YouTube videos will not embed properly on the site. You can post links to YouTube but they will not display as a preview that you can click and play on the site. This would appear to be something YouTube have changed at their end. Please bear with me while I find a solution.
For the time being If you post the link in “Another Link” field it will at least be a ‘clickable’ link which will take the reader to YouTube so they can watch the clip there.