2.2.2: Unable to allocate memory for pool. in .../core/Loader.php (no replies)

Piwik was running stable until the update to version 2.2.2. Now, I get an error message in the "Pages" widget on the Dashboard page. The same error message appears multiple times (~20 times). It looks as if the error occurs when starting the first time. When reloading the Dashboard page, everything works fine.

Below please find the full backtrace which appears in the "Pages" widget. Please note that I've replaced the path of the piwik installation with "blubber" in the backtrace.

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Unable to allocate memory for pool. in /web/1/000/021/500/50509/htdocs/_vectrex/piwik/core/Loader.php

There is an error. Please report the message (Piwik 2.2.2) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Warning: require_once() [function.require-once]: Unable to allocate memory for pool. in /web/1/000/021/500/50509/htdocs/_vectrex/piwik/core/Loader.php on line 98

Backtrace -->

#0 Piwik\Error::errorHandler(...) called at [/web/blubber/piwik/core/Loader.php:98]
#1 Piwik\Loader::tryToLoadClass(...) called at [/web/blubber/piwik/core/Loader.php:98]
#2 Piwik\Loader::tryToLoadClass(...) called at [/web/blubber/piwik/core/Loader.php:84]
#3 Piwik\Loader::loadClass(...) called at [/web/blubber/piwik/core/Loader.php:114]
#4 Piwik\Loader::autoload(...) called at [:]
#5 spl_autoload_call(...) called at [/web/blubber/piwik/plugins/Goals/Goals.php:176]
#6 Piwik\Plugins\Goals\Goals->getReportMetadata(...) called at [:]
#7 call_user_func_array(...) called at [/web/blubber/piwik/core/EventDispatcher.php:98]
#8 Piwik\EventDispatcher->postEvent(...) called at [/web/blubber/piwik/core/Piwik.php:767]
#9 Piwik\Piwik::postEvent(...) called at [/web/blubber/piwik/plugins/API/ProcessedReport.php:238]
#10 Piwik\Plugins\API\ProcessedReport->getReportMetadata(...) called at [/web/blubber/piwik/plugins/API/API.php:395]
#11 Piwik\Plugins\API\API->getReportMetadata(...) called at [/web/blubber/piwik/plugins/API/API.php:425]
#12 Piwik\Plugins\API\API->get(...) called at [:]
#13 call_user_func_array(...) called at [/web/blubber/piwik/core/API/Proxy.php:209]
#14 Piwik\API\Proxy->call(...) called at [/web/blubber/piwik/core/API/Request.php:215]
#15 Piwik\API\Request->process(...) called at [/web/blubber/piwik/plugins/CoreVisualizations/Visualizations/HtmlTable.php:70]
#16 Piwik\Plugins\CoreVisualizations\Visualizations\HtmlTable->beforeRender(...) called at [/web/blubber/piwik/core/Plugin/Visualization.php:173]
#17 Piwik\Plugin\Visualization->buildView(...) called at [/web/blubber/piwik/core/Plugin/ViewDataTable.php:375]
#18 Piwik\Plugin\ViewDataTable->render(...) called at [/web/blubber/piwik/core/Plugin/Controller.php:281]
#19 Piwik\Plugin\Controller->renderReport(...) called at [/web/blubber/piwik/plugins/Actions/Controller.php:89]
#20 Piwik\Plugins\Actions\Controller->getPageUrls(...) called at [:]
#21 call_user_func_array(...) called at [/web/blubber/piwik/core/FrontController.php:500]
#22 Piwik\FrontController->doDispatch(...) called at [/web/blubber/piwik/core/FrontController.php:85]
#23 Piwik\FrontController->dispatch(...) called at [/web/blubber/piwik/core/dispatch.php:34]
#24 require_once(...) called at [/web/blubber/piwik/index.php:47]