MediaWiki internal error.

Original exception: exception 'DBUnexpectedError' with message 'Error in fetchObject(): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111) (localhost)' in /home/encyclopedia/public_html/w/includes/db/Database.php:788
Stack trace:
#0 /home/encyclopedia/public_html/w/extensions/SemanticMediaWiki/includes/storage/SMW_SQLStore2_Queries.php(400): Database->fetchObject(false)
#1 /home/encyclopedia/public_html/w/extensions/SemanticMediaWiki/includes/storage/SMW_SQLStore2_Queries.php(263): SMWSQLStore2QueryEngine->getInstanceQueryResult(Object(SMWQuery), 3)
#2 /home/encyclopedia/public_html/w/extensions/SemanticMediaWiki/includes/storage/SMW_SQLStore2.php(979): SMWSQLStore2QueryEngine->getQueryResult(Object(SMWQuery))
#3 /home/encyclopedia/public_html/w/extensions/IndexFunction/IndexFunction_body.php(40): SMWSQLStore2->getQueryResult(Object(SMWQuery))
#4 /home/encyclopedia/public_html/w/extensions/IndexFunction/IndexFunction_body.php(208): IndexFunction->queryIndexes()
#5 /home/encyclopedia/public_html/w/extensions/IndexFunction/IndexFunction_body.php(374): IndexFunction::newFromTitle(Object(Title))
#6 [internal function]: IndexFunctionHooks::blueLinkIndexes(Object(SkinMonoBook), Object(Title), Array, 'Alfred Berling', Array, NULL)
#7 /home/encyclopedia/public_html/w/includes/Hooks.php(117): call_user_func_array(Array, Array)
#8 /home/encyclopedia/public_html/w/includes/Linker.php(222): wfRunHooks('LinkEnd', Array)
#9 /home/encyclopedia/public_html/w/includes/Linker.php(445): Linker->link(Object(Title), 'Alfred Berling', Array, Array)
#10 /home/encyclopedia/public_html/w/includes/Linker.php(339): Linker->makeLinkObj(Object(Title), 'Alfred Berling', '', '')
#11 /home/encyclopedia/public_html/w/includes/Linker.php(1339): Linker->makeLink('Alfred Berling', 'Alfred Berling', '', '')
#12 [internal function]: Linker->formatLinksInCommentCallback(Array)
#13 /home/encyclopedia/public_html/w/includes/Linker.php(1302): preg_replace_callback('/\[\[:?(.*?)(\|...', Array, 'moved [[Alfred ...')
#14 /home/encyclopedia/public_html/w/includes/Linker.php(1211): Linker->formatLinksInComment('moved [[Alfred ...')
#15 /home/encyclopedia/public_html/w/includes/Linker.php(1363): Linker->formatComment('moved [[Alfred ...', Object(Title), false)
#16 /home/encyclopedia/public_html/w/includes/Linker.php(1382): Linker->commentBlock('moved [[Alfred ...', Object(Title), false)
#17 /home/encyclopedia/public_html/w/includes/PageHistory.php(295): Linker->revComment(Object(Revision), false, true)
#18 /home/encyclopedia/public_html/w/includes/PageHistory.php(594): PageHistory->historyLine(Object(stdClass), Object(stdClass), 1, false, true, true)
#19 /home/encyclopedia/public_html/w/includes/Pager.php(290): PageHistoryPager->formatRow(Object(stdClass))
#20 /home/encyclopedia/public_html/w/includes/PageHistory.php(142): IndexPager->getBody()
#21 /home/encyclopedia/public_html/w/includes/Wiki.php(523): PageHistory->history()
#22 /home/encyclopedia/public_html/w/includes/Wiki.php(63): MediaWiki->performAction(Object(OutputPage), Object(Article), Object(Title), Object(User), Object(WebRequest))
#23 /home/encyclopedia/public_html/w/index.php(118): MediaWiki->initialize(Object(Title), Object(Article), Object(OutputPage), Object(User), Object(WebRequest))
#24 {main}

Exception caught inside exception handler: exception 'DBUnexpectedError' with message 'Error in numRows(): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111) (localhost)' in /home/encyclopedia/public_html/w/includes/db/Database.php:822
Stack trace:
#0 /home/encyclopedia/public_html/w/extensions/SemanticForms/includes/SF_LinkUtils.inc(265): Database->numRows(false)
#1 /home/encyclopedia/public_html/w/extensions/SemanticForms/includes/SF_LinkUtils.inc(280): SFLinkUtils::getCategoriesForArticle(Object(SkinMonoBook))
#2 /home/encyclopedia/public_html/w/extensions/SemanticForms/includes/SF_FormEditTab.php(25): SFLinkUtils::getFormForArticle(Object(SkinMonoBook))
#3 [internal function]: SFFormEditTab::displayTab(Object(SkinMonoBook), Array)
#4 /home/encyclopedia/public_html/w/includes/Hooks.php(117): call_user_func_array(Array, Array)
#5 /home/encyclopedia/public_html/w/includes/SkinTemplate.php(804): wfRunHooks('SkinTemplateTab...', Array)
#6 /home/encyclopedia/public_html/w/includes/SkinTemplate.php(437): SkinTemplate->buildContentActionUrls()
#7 /home/encyclopedia/public_html/w/includes/OutputPage.php(968): SkinTemplate->outputPage(Object(OutputPage))
#8 /home/encyclopedia/public_html/w/includes/Exception.php(159): OutputPage->output()
#9 /home/encyclopedia/public_html/w/includes/Exception.php(186): MWException->reportHTML()
#10 /home/encyclopedia/public_html/w/includes/Exception.php(284): MWException->report()
#11 /home/encyclopedia/public_html/w/includes/Exception.php(344): wfReportException(Object(DBUnexpectedError))
#12 [internal function]: wfExceptionHandler(Object(DBUnexpectedError))
#13 {main}