Thread:Project:Support desk/Error when trying to "Edit" wiki/reply (25)

Note, editing with notepad will only add a BOM, which will just give a warning (The famous headers already sent - which is annoying and a pain, and mildly break some things), but it won't kill your site. If your wiki is down, its due to some other reason than editing LocalSettings.php with notepad.

FCKeditor is a poorly maintained extension that never worked well in the first place (That is just my own humble opinion though), but is probably broken on newer mediawiki.