Hey, I had the same problem and following the abovementioned Icamp’s suggestion it worked fine: “…Following step #2 only turns off the rich text editor for ‘users’ but if you’re the admin trying to paste the YouTube code you must turn off rich text editing under: users>your profile “.
Once it is published you can turn this option on again. You can see how I did it in https://www.hotelblog.es
Thank you guys for your help!