Important Anyone help? Youtube embed code with preview ok, but when click "submit" get 404 error

I paste the embedd code between video type/provider option, then preview = ok, but when click on "submit" the result is a 404 error page:

---

The website declined to show this webpage
HTTP 403
Most likely causes:
This website requires you to log in.

What you can try:
Go back to the previous page.

More information

This error (HTTP 403 Forbidden) means that Internet Explorer was able to connect to the website, but it does not have permission to view the webpage.

For more information about HTTP errors, see Help.

---

The url displayed is: https://www.{our_web_site}.com/index.php?option=com_kunena&Itemid=60&catid=28&func=post&lang=en

And the message is not posted to the forum.

k.

Can you give bbcode example?

It's a standard embed that works on the Kunena site here. It used to work when Fireboard was installed and then broke for some reason.

SEF enabled?

Yes SEF is enabled. Using sh404sef

With that said, can it be be made to work?

I'm not an expert on sh404sef, but trying to understand how to manipulate it where possible.

k.

I don't know. I don't use it. But my guess is that it's causing your problems. Actually it causes a lot of problems from what I've read.