MediaWiki internal error.

Original exception: [a473f4c5f6663319140b0c29] /index.php?title=Prova&diff=prev&oldid=1359 MWException from line 4276 of /var/lib/mediawiki/includes/parser/Parser.php: Tag hook for select_exam is not callable

Backtrace:
#0 /var/lib/mediawiki/includes/parser/Preprocessor_DOM.php(1260): Parser->extensionSubstitution(array, PPFrame_DOM)
#1 /var/lib/mediawiki/includes/parser/Parser.php(3380): PPFrame_DOM->expand(DOMElement, integer)
#2 /var/lib/mediawiki/includes/parser/Parser.php(1261): Parser->replaceVariables(string)
#3 /var/lib/mediawiki/includes/parser/Parser.php(452): Parser->internalParse(string)
#4 /var/lib/mediawiki/includes/content/WikitextContent.php(331): Parser->parse(string, Title, ParserOptions, boolean, boolean, integer)
#5 /var/lib/mediawiki/includes/content/AbstractContent.php(497): WikitextContent->fillParserOutput(Title, integer, ParserOptions, boolean, ParserOutput)
#6 /var/lib/mediawiki/includes/poolcounter/PoolWorkArticleView.php(139): AbstractContent->getParserOutput(Title, integer, ParserOptions)
#7 /var/lib/mediawiki/includes/poolcounter/PoolCounterWork.php(123): PoolWorkArticleView->doWork()
#8 /var/lib/mediawiki/includes/page/WikiPage.php(1079): PoolCounterWork->execute()
#9 /var/lib/mediawiki/includes/diff/DifferenceEngine.php(636): WikiPage->getParserOutput(ParserOptions, integer)
#10 /var/lib/mediawiki/includes/diff/DifferenceEngine.php(614): DifferenceEngine->getParserOutput(WikiPage, Revision)
#11 /var/lib/mediawiki/includes/diff/DifferenceEngine.php(456): DifferenceEngine->renderNewRevision()
#12 /var/lib/mediawiki/includes/page/Article.php(794): DifferenceEngine->showDiffPage(boolean)
#13 /var/lib/mediawiki/includes/page/Article.php(503): Article->showDiffPage()
#14 /var/lib/mediawiki/includes/actions/ViewAction.php(44): Article->view()
#15 /var/lib/mediawiki/includes/MediaWiki.php(493): ViewAction->show()
#16 /var/lib/mediawiki/includes/MediaWiki.php(288): MediaWiki->performAction(Article, Title)
#17 /var/lib/mediawiki/includes/MediaWiki.php(735): MediaWiki->performRequest()
#18 /var/lib/mediawiki/includes/MediaWiki.php(509): MediaWiki->main()
#19 /var/lib/mediawiki/index.php(43): MediaWiki->run()
#20 {main}

Exception caught inside exception handler: [a473f4c5f6663319140b0c29] /index.php?title=Prova&diff=prev&oldid=1359 MWException from line 4276 of /var/lib/mediawiki/includes/parser/Parser.php: Tag hook for select_exam is not callable

Backtrace:
#0 /var/lib/mediawiki/includes/parser/Preprocessor_DOM.php(1260): Parser->extensionSubstitution(array, PPFrame_DOM)
#1 /var/lib/mediawiki/includes/parser/Parser.php(3380): PPFrame_DOM->expand(DOMElement, integer)
#2 /var/lib/mediawiki/includes/parser/Parser.php(1261): Parser->replaceVariables(string)
#3 /var/lib/mediawiki/includes/parser/Parser.php(452): Parser->internalParse(string)
#4 /var/lib/mediawiki/skins/bootstrap-mediawiki/BootstrapMediaWiki.skin.php(495): Parser->parse(string, Title, ParserOptions)
#5 /var/lib/mediawiki/skins/bootstrap-mediawiki/BootstrapMediaWiki.skin.php(244): BootstrapMediaWikiTemplate->includePage(string)
#6 /var/lib/mediawiki/includes/skins/SkinTemplate.php(248): BootstrapMediaWikiTemplate->execute()
#7 /var/lib/mediawiki/includes/OutputPage.php(2335): SkinTemplate->outputPage()
#8 /var/lib/mediawiki/includes/exception/MWException.php(206): OutputPage->output()
#9 /var/lib/mediawiki/includes/exception/MWException.php(246): MWException->reportHTML()
#10 /var/lib/mediawiki/includes/exception/MWExceptionHandler.php(69): MWException->report()
#11 /var/lib/mediawiki/includes/exception/MWExceptionHandler.php(180): MWExceptionHandler::report(MWException)
#12 /var/lib/mediawiki/includes/MediaWiki.php(518): MWExceptionHandler::handleException(MWException)
#13 /var/lib/mediawiki/index.php(43): MediaWiki->run()
#14 {main}