During a botched deployment of 242661, the fatal errors were always preceded by an "Undefined index" notice. The fatal error has since been fixed, but I suspect the notice might need some attention.
Oct 5 20:54:55 mw1210: #012Notice: Undefined index: function in /srv/mediawiki/php-1.27.0-wmf.1/includes/exception/MWExceptionHandler.php on line 386 Oct 5 20:54:55 mw1210: #012Fatal error: Class undefined: ZeroBanner\ResourceLoader in /srv/mediawiki/php-1.27.0-wmf.1/extensions/ZeroBanner/includes/ZeroSpecialPage.php on line 519