Was running fine until the following error.
There is an error. Please report the message (Piwik 1.11.1) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).
Warning: require_once(): Unable to allocate memory for pool. in /var/www/html/wordpress/piwik/core/Loader.php on line 71
Backtrace -->
#0 Piwik_ErrorHandler(…) called at [/var/www/html/wordpress/piwik/core/Loader.php:71]
#1 Piwik_Loader::loadClass(…) called at [/var/www/html/wordpress/piwik/core/Loader.php:71]
#2 Piwik_Loader::loadClass(…) called at [/var/www/html/wordpress/piwik/core/Loader.php:108]
#3 Piwik_Loader::autoload(…) called at [:]
#4 spl_autoload_call(…) called at [/var/www/html/wordpress/piwik/core/ArchiveProcessing.php:241]
#5 Piwik_ArchiveProcessing::factory(…) called at [/var/www/html/wordpress/piwik/core/Archive/Single.php:211]
#6 Piwik_Archive_Single->prepareArchive(…) called at [/var/www/html/wordpress/piwik/core/Archive/Single.php:265]
#7 Piwik_Archive_Single->get(…) called at [/var/www/html/wordpress/piwik/core/Archive/Single.php:529]
#8 Piwik_Archive_Single->getDataTable(…) called at [/var/www/html/wordpress/piwik/core/Archive.php:368]
#9 Piwik_Archive::getDataTableFromArchive(…) called at [/var/www/html/wordpress/piwik/plugins/Referers/API.php:39]
#10 Piwik_Referers_API->getDataTable(…) called at [/var/www/html/wordpress/piwik/plugins/Referers/API.php:139]
#11 Piwik_Referers_API->getKeywords(…) called at [:]
#12 call_user_func_array(…) called at [/var/www/html/wordpress/piwik/core/API/Proxy.php:189]
#13 Piwik_API_Proxy->call(…) called at [/var/www/html/wordpress/piwik/core/API/Request.php:127]
#14 Piwik_API_Request->process(…) called at [/var/www/html/wordpress/piwik/core/ViewDataTable.php:431]
#15 Piwik_ViewDataTable->loadDataTableFromAPI(…) called at [/var/www/html/wordpress/piwik/core/ViewDataTable/HtmlTable.php:80]
#16 Piwik_ViewDataTable_HtmlTable->main(…) called at [/var/www/html/wordpress/piwik/core/Controller.php:151]
#17 Piwik_Controller->renderView(…) called at [/var/www/html/wordpress/piwik/plugins/Referers/Controller.php:254]
#18 Piwik_Referers_Controller->getKeywords(…) called at [:]
#19 call_user_func_array(…) called at [/var/www/html/wordpress/piwik/core/FrontController.php:136]
#20 Piwik_FrontController->dispatch(…) called at [/var/www/html/wordpress/piwik/index.php:52]