エクステンションまたは LocalSettings.php の設定に問題があるのではないでしょうか。
以下のエラーログを参考にご修正ください。
[Fri Jul 08 19:04:19 2011] [error] [client 114.178.149.207] PHP Notice:  Use of undefined constant SAN - assumed 'SAN' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531, referer: http://myht.org/modules/d3forum/index.php?topic_id=402
[Fri Jul 08 19:04:19 2011] [error] [client 114.178.149.207] PHP Fatal error:  Call to undefined method User::getStubThreshold() in /home/mysite/homes/wikiparody.myht.org/html/includes/Article.php on line 1465, referer: http://myht.org/modules/d3forum/index.php?topic_id=402
[Fri Jul 08 19:05:39 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(extensions/CheckUser/CheckUser.php): failed to open stream: No such file or directory in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:39 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(): Failed opening 'extensions/CheckUser/CheckUser.php' for inclusion (include_path='/home/mysite/homes/wikiparody.myht.org/html:/home/mysite/homes/wikiparody.myht.org/html/includes:/home/mysite/homes/wikiparody.myht.org/html/languages:.:/usr/share/pear:/usr/share/php') in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(extensions/CheckUser/CheckUser.php): failed to open stream: No such file or directory in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(): Failed opening 'extensions/CheckUser/CheckUser.php' for inclusion (include_path='/home/mysite/homes/wikiparody.myht.org/html:/home/mysite/homes/wikiparody.myht.org/html/includes:/home/mysite/homes/wikiparody.myht.org/html/languages:.:/usr/share/pear:/usr/share/php') in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] PHP Notice:  Use of undefined constant Nanashi - assumed 'Nanashi' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] PHP Notice:  Use of undefined constant SAN - assumed 'SAN' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] PHP Fatal error:  Call to undefined method User::getStubThreshold() in /home/mysite/homes/wikiparody.myht.org/html/includes/Article.php on line 1465, referer: http://myht.org/modules/mysite/admin/index.php?q=hanakayu
[Fri Jul 08 19:05:40 2011] [error] [client 114.178.149.207] File does not exist: /home/mysite/homes/wikiparody.myht.org/html/favicon.ico
[Fri Jul 08 19:05:48 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(extensions/CheckUser/CheckUser.php): failed to open stream: No such file or directory in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134
[Fri Jul 08 19:05:48 2011] [error] [client 114.178.149.207] PHP Warning:  include_once(): Failed opening 'extensions/CheckUser/CheckUser.php' for inclusion (include_path='/home/mysite/homes/wikiparody.myht.org/html:/home/mysite/homes/wikiparody.myht.org/html/includes:/home/mysite/homes/wikiparody.myht.org/html/languages:.:/usr/share/pear:/usr/share/php') in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134
[Fri Jul 08 19:05:48 2011] [error] [client 114.178.149.207] PHP Notice:  Use of undefined constant Nanashi - assumed 'Nanashi' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531
[Fri Jul 08 19:05:48 2011] [error] [client 114.178.149.207] PHP Notice:  Use of undefined constant SAN - assumed 'SAN' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531
[Fri Jul 08 19:05:48 2011] [error] [client 114.178.149.207] PHP Fatal error:  Call to undefined method User::getStubThreshold() in /home/mysite/homes/wikiparody.myht.org/html/includes/Article.php on line 1465
[Fri Jul 08 19:09:51 2011] [error] [client 119.235.237.93] PHP Warning:  include_once(extensions/CheckUser/CheckUser.php): failed to open stream: No such file or directory in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134
[Fri Jul 08 19:09:51 2011] [error] [client 119.235.237.93] PHP Warning:  include_once(): Failed opening 'extensions/CheckUser/CheckUser.php' for inclusion (include_path='/home/mysite/homes/wikiparody.myht.org/html:/home/mysite/homes/wikiparody.myht.org/html/includes:/home/mysite/homes/wikiparody.myht.org/html/languages:.:/usr/share/pear:/usr/share/php') in /home/mysite/homes/wikiparody.myht.org/html/LocalSettings.php on line 134
[Fri Jul 08 19:09:51 2011] [error] [client 119.235.237.93] PHP Notice:  Use of undefined constant Nanashi - assumed 'Nanashi' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531
[Fri Jul 08 19:09:51 2011] [error] [client 119.235.237.93] PHP Notice:  Use of undefined constant SAN - assumed 'SAN' in /home/mysite/homes/wikiparody.myht.org/html/includes/User.php on line 1531
[Fri Jul 08 19:09:51 2011] [error] [client 119.235.237.93] PHP Fatal error:  Call to undefined method User::getStubThreshold() in /home/mysite/homes/wikiparody.myht.org/html/includes/Article.php on line 1465