You tube videos are being stripped from editor

I have installed a Multi Site wordpress and have a couple of client who set up pages when they try and ad you tube videos the video code is being stripped from the page when it is saved.

I thought it was the Ultimate TinyMCE editor I was using so I installed TinyMCE Advanced and still had the same issue

so I thought maybe the multi site installation was faulty so I installed a clean Multisite on a new domain and added the TinyMCE Advanced editor and the client still had the same results video code being stripped from the page or post would this be a multi site issue

thanks
steve