Нужно больше информации. О том как вывести ошибку целиком написано тут:
http://mediawiki.ru/forum/threads/112/#post-2813
[c93e2a874d5a2a011d3b5647] /index.php?title=%D0%9A%D0%B0%D1%82%D0%B5%D0%B3%D0%BE%D1%80%D0%B8%D1%8F:%D0%90%D1%80%D1%85%D0%B8%D0%B2&action=submit Error from line 30 of /home/user/web/My_site/public_html/extensions/Widgets/WidgetRenderer.php: Call to undefined method Smarty::addPluginsDir()
Backtrace:
#0 /home/user/web/My_site/public_html/includes/parser/Parser.php(3383): WidgetRenderer::renderWidget(Parser, string, string, string, string, string, string, string, string, string, string, string)
#1 /home/user/web/My_site/public_html/includes/parser/Parser.php(3106): Parser->callParserFunction(PPFrame_DOM, string, array)
#2 /home/user/web/My_site/public_html/includes/parser/Preprocessor_DOM.php(1229): Parser->braceSubstitution(array, PPFrame_DOM)
#3 /home/user/web/My_site/public_html/includes/parser/Parser.php(2921): PPFrame_DOM->expand(DOMElement, integer)
#4 /home/user/web/My_site/public_html/includes/parser/Parser.php(1277): Parser->replaceVariables(string)
#5 /home/user/web/My_site/public_html/includes/parser/Parser.php(451): Parser->internalParse(string)
#6 /home/user/web/My_site/public_html/includes/content/WikitextContent.php(329): Parser->parse(string, Title, ParserOptions, boolean, boolean, NULL)
#7 /home/user/web/My_site/public_html/includes/content/AbstractContent.php(516): WikitextContent->fillParserOutput(Title, NULL, ParserOptions, boolean, ParserOutput)
#8 /home/user/web/My_site/public_html/includes/page/WikiPage.php(2080): AbstractContent->getParserOutput(Title, NULL, ParserOptions)
#9 /home/user/web/My_site/public_html/extensions/SpamBlacklist/SpamBlacklistHooks.php(44): WikiPage->prepareContentForEdit(WikitextContent)
#10 /home/user/web/My_site/public_html/includes/Hooks.php(177): SpamBlacklistHooks::filterMergedContent(RequestContext, WikitextContent, Status, string, User, boolean)
#11 /home/user/web/My_site/public_html/includes/Hooks.php(205): Hooks::callHook(string, array, array, NULL)
#12 /home/user/web/My_site/public_html/includes/EditPage.php(1688): Hooks::run(string, array)
#13 /home/user/web/My_site/public_html/includes/EditPage.php(1987): EditPage->runPostMergeFilters(WikitextContent, Status, User)
#14 /home/user/web/My_site/public_html/includes/EditPage.php(1514): EditPage->internalAttemptSave(NULL, boolean)
#15 /home/user/web/My_site/public_html/includes/EditPage.php(667): EditPage->attemptSave(NULL)
#16 /home/user/web/My_site/public_html/includes/actions/EditAction.php(60): EditPage->edit()
#17 /home/user/web/My_site/public_html/includes/actions/SubmitAction.php(38): EditAction->show()
#18 /home/user/web/My_site/public_html/includes/MediaWiki.php(499): SubmitAction->show()
#19 /home/user/web/My_site/public_html/includes/MediaWiki.php(293): MediaWiki->performAction(CategoryPage, Title)
#20 /home/user5web/My_site/public_html/includes/MediaWiki.php(851): MediaWiki->performRequest()
#21 /home/user/web/My_site/public_html/includes/MediaWiki.php(523): MediaWiki->main()
#22 /home/user/web/My_site/public_html/index.php(43): MediaWiki->run()
#23 {main}