https://en.wikipedia.org/wiki/Wikipedia:Ambassadors/Courses/Theater_History_from_1642_%28Amy_E_Hughes%29/Timeline?redirect=no is a redirect to https://en.wikipedia.org/wiki/Education_Program:CUNY,_Brooklyn_College/Theater_History_from_1642_%28Spring_2013%29 which exists. However if you try to use the redirect directly (https://en.wikipedia.org/wiki/Wikipedia:Ambassadors/Courses/Theater_History_from_1642_%28Amy_E_Hughes%29/Timeline), the "Wikimedia Foundation error" screen comes up with:
PHP fatal error in /usr/local/apache/common-local/php-1.21wmf8/includes/Wiki.php line 387:
Call to undefined method CoursePage::loadPageData()
Version: unspecified
Severity: critical