You will usually notice this problem when saving the post never ends:
Your server security is not allowing you to save any information via POST that contains the keyword “iframe”.
Since Youtube normal embeds will work using the iframe tag, your server will return a -403 forbidden error- when trying to save the post.
You should open a support ticket in your hosting provider asking them to allow the iframe tag to be sent via POST protocol.
If your hosting support is not helping, you can use this workaround to still embed Youtube videos.
1. Select Insert->Media->Embed
2. Copy and paste the code below replacing your Youtube video ID.
3. The Youtube video ID can be extracted from the original URL: https://www.youtube.com/watch?v=YOUTUBE-VIDEO-ID