Thread:Project:Support desk/Call to a member function addMessage() on a non-object/reply

Hi!

You can comment the line in LocalSettings.php, which includes/requires EmbedVideo.php. This will deactivate the extension, but at least your wiki will show up again.

According to Extension:EmbedVideo this extension is not (yet) compatible with MediaWiki 1.21. This has also been reported in the issue tracker, but the developer has not yet fixed it. The file EmbedVideo.php, which I found here does not have 84 lines, so I cannot say, what causes the error for you.