This might be a duplicate of an already fixed bug... It looks familiar. Feel free to close as dupe, just tidying up after a list aggregated of errors...

[22-Nov-2013 10:17:31] Fatal error: Class 'Wikibase\InfoActionHookHandler' not found at /usr/local/apache/common-local/php-1.23wmf5/extensions/Wikibase/client/WikibaseClient.hooks.php on line 696
Server: mw1162
Method: GET
URL: http://test2.wikipedia.org/w/index.php?title=Main_Page&action=info
Backtrace:
#0 /usr/local/apache/common-local/php-1.23wmf5/extensions/Wikibase/client/WikibaseClient.hooks.php(696): Wikibase\ClientHooks::onInfoAction()
#1 [internal function]: Wikibase\ClientHooks::onInfoAction(Object(RequestContext), Array)
#2 /usr/local/apache/common-local/php-1.23wmf5/includes/Hooks.php(199): call_user_func_array('\Wikibase\Clien...', Array)
#3 /usr/local/apache/common-local/php-1.23wmf5/includes/GlobalFunctions.php(4033): Hooks::run('InfoAction', Array)
#4 /usr/local/apache/common-local/php-1.23wmf5/includes/actions/InfoAction.php(117): wfRunHooks('InfoAction', Array)
#5 /usr/local/apache/common-local/php-1.23wmf5/includes/Action.php(567): InfoAction->onView()
#6 /usr/local/apache/common-local/php-1.23wmf5/includes/Wiki.php(441): FormlessAction->show()
#7 /usr/local/apache/common-local/php-1.23wmf5/includes/Wiki.php(305): MediaWiki->performAction(Object(Article), Object(Title))
#8 /usr/local/apache/common-local/php-1.23wmf5/includes/Wiki.php(596): MediaWiki->performRequest()
#9 /usr/local/apache/common-local/php-1.23wmf5/includes/Wiki.php(460): MediaWiki->main()
#10 /usr/local/apache/common-local/php-1.23wmf5/index.php(49): MediaWiki->run()
#11 /usr/local/apache/common-local/w/index.php(3): require('/usr/local/apac...')
#12 {main}

Version: master
Severity: normal