Things have Changed on Youtube, so forget how you used to do it. They're trying to switch everyone over to their new embed code iframe, but many forums like this one on Network54 are not using it yet. We're not happy about this but here here the work around.
Go to the Youtube Page with the video you want to share. For example let's pick this video of our Green Machine on Youtube.
Here is the page link URL:
Copy the video 11 digit code (after the v= sign) from the Youtube video you want to post. IN this case it's DLxLnMnBFd4
NOW COPY THE CODE from the page on this link...
and then replace the 00000000000 in 2 spots with your 11 digit code.
Here is a photo of the text with the 2 code areas in RED. Paste the corrected code into the forum and the video will show as embedded.