I am going to go a bit off topic, and say that statement actually made me laugh. :)
Thanks for that, and sorry to hear you are having such trouble. If I had any idea I would share, but alas I don't. :(

That made me chuckle too.

It may have something to do with when you upgraded to vB 5.11. Possibly something was broken that was not broken before. Its not unusual for that to happen on some sites from a new upgrade. Have you asked on vbulletin.com about this or searched there to see if its an issue with this upgrade?

Yeah they were looking at it but couldn't find the issue initially so i'm apparently waiting until after the holidays for vb staff to look at it when they start working again.

Here's my theory, at one stage the video button in the advanced tab wouldn't work.
So instead of putting up a video via the video button, you can add a video using the "Post Link" paperclip.

So members alternated between using the video button and the post link button.

Now if I go to edit one of the posts with video and try and delete the video it doesn't allow that, I need to insert a valid url for it to work.
So I can't delete a url unless I add another url. it says, "error please enter a valid url".

Now when I click edit to edit a post with video it looks like this..

http://i44.photobucket.com/albums/f1...ps347ab3a6.png

Can you see the blue box top left corner? hovering over it says "Post a Video"
but it doesn't work, it's just a picture, not a button.

The post below, I added the video using the video button in advanced editor.
click edit post and it looks like this..

http://i44.photobucket.com/albums/f1...ps7c4d00f5.png

as you can see it does not have the blue box on the top left, and I can delete the video and replace with text no problem.

So I think there was a conflict between the two possibilities of adding a video, one via video button, the other via url button.
so now no matter which version I upgrade to the error is like built in.

I'm thinking maybe the only way to fix it is to delete all posts with video's completely.
from that point it might fix itself?

I don't know it might but if there is an error built into the software its also likely that deleting those posts will not help you either and it will continue to do the same thing even with new posts. Is there a way that you can limit how members post videos? Like only allow it via the link or the button? I do not run vB5 so I have not looked at it to see.

Not sure if I could get everyone to go one way or the other, it doesn't seem to be any different now as they both show a black screen.

I think a video button would be easier if it was visible like the other tabs when creating a new post.
already there is: share photo's - Post Link - Insert Poll, so it's common sense to put "Insert Video" that's why they go looking in the advanced tab for it.

it's just too difficult for me, what eats me is most vb5 sites work ok with video's and I just have a basic forum. oh well, might just go and stand on my head afterall.

Well what I was thinking was if you could limit the users to only use one or the other the perhaps you can delete the posts/threads and make sure that you have it in place to have them only allowed to use a certain way to put the videos into a post. That "might" work but IDK. It might not too and you would have deleted the post for nothing.

Is your server set up to block any sites? The youtube video thumbnail is created by google - it's from ytimg.com (or one of it's other servers). If you are blocking google, then perhaps the thumbnail creation is being blocked.

<a href="http://tracker.vbulletin.com/browse/VBV-13599" target="_blank">http://tracker.vbulletin.com/browse/VBV-13599</a> should be fixed in 5.1.5

Though, it seems the specific customer was missing cURL in their PHP (not the server).

No I don't believe i'm blocking google.
I have google adsense on my site and google seems to send lots of bots to my site so i'd say it's not blocked.

But you say on the server? should I be asking my host? urljet?
what do I ask them?

I tried using bbcode, Example - [youtube]xxxxxxxxxx[/youtube]
It doesn't work.

Would I need to do the following? does that work in vb5?

Admin CP -> Custom BB Codes -> Add New BB Code

Title - YouTube
Tag - youtube
Replacement:

Code:
<object width="425" height="350"><param name="movie" value="http://www.youtube.com/v/{param}"></param><embed src="http://www.youtube.com/v/{param}" type="application/x-shockwave-flash" width="425" height="350"></embed></object>

Well hopefully 5.1.5 solves it for you as Zachary suggests.