Automatic Update to Piwik 2.9.0: Error Widget includes (no replies)

Hi,

automatic update to Piwik 2.9.0 gives me following error on loading most of the included widgets:

Warning: require_once(/home/xxx/plugins/UserSettings/functions.php): failed to open stream: Datei oder Verzeichnis nicht gefunden in /home/xxx/plugins/UserSettings/Archiver.php on line 18

Backtrace:

#0 Piwik\Error::errorHandler(...) called at [/home/xxx/plugins/UserSettings/Archiver.php:18]
#1 require_once(...) called at [/home/xxx/plugins/UserSettings/Archiver.php:18]
#2 include(...) called at [/home/xxx/vendor/composer/ClassLoader.php:382]
#3 Composer\Autoload\includeFile(...) called at [/home/xxx/vendor/composer/ClassLoader.php:274]
#4 Composer\Autoload\ClassLoader->loadClass(...) called at [:]
#5 spl_autoload_call(...) called at [:]
#6 class_exists(...) called at [/home/xxx/core/ArchiveProcessor/PluginsArchiver.php:150]
#7 Piwik\ArchiveProcessor\PluginsArchiver::getPluginArchiverClass(...) called at [/home/xxx/core/ArchiveProcessor/PluginsArchiver.php:140]
#8 Piwik\ArchiveProcessor\PluginsArchiver->getPluginArchivers(...) called at [/home/xxx/core/ArchiveProcessor/PluginsArchiver.php:89]
#9 Piwik\ArchiveProcessor\PluginsArchiver->callAggregateAllPlugins(...) called at [/home/xxx/core/ArchiveProcessor/Loader.php:122]
#10 Piwik\ArchiveProcessor\Loader->prepareAllPluginsArchive(...) called at [/home/xxx/core/ArchiveProcessor/Loader.php:72]
#11 Piwik\ArchiveProcessor\Loader->prepareArchive(...) called at [/home/xxx/core/Archive.php:801]
#12 Piwik\Archive->prepareArchive(...) called at [/home/xxx/core/Archive.php:614]
#13 Piwik\Archive->cacheArchiveIdsAfterLaunching(...) called at [/home/xxx/core/Archive.php:568]
#14 Piwik\Archive->getArchiveIds(...) called at [/home/xxx/core/Archive.php:508]
#15 Piwik\Archive->get(...) called at [/home/xxx/core/Archive.php:348]
#16 Piwik\Archive->getDataTableFromNumeric(...) called at [/home/xxx/core/ArchiveProcessor.php:502]
#17 Piwik\ArchiveProcessor->getAggregatedNumericMetrics(...) called at [/home/xxx/core/ArchiveProcessor.php:260]
#18 Piwik\ArchiveProcessor->aggregateNumericMetrics(...) called at [/home/xxx/core/ArchiveProcessor/PluginsArchiver.php:203]
#19 Piwik\ArchiveProcessor\PluginsArchiver->aggregateMultipleVisitsMetrics(...) called at [/home/xxx/core/ArchiveProcessor/PluginsArchiver.php:63]
#20 Piwik\ArchiveProcessor\PluginsArchiver->callAggregateCoreMetrics(...) called at [/home/xxx/core/ArchiveProcessor/Loader.php:97]
#21 Piwik\ArchiveProcessor\Loader->prepareCoreMetricsArchive(...) called at [/home/xxx/core/ArchiveProcessor/Loader.php:71]
#22 Piwik\ArchiveProcessor\Loader->prepareArchive(...) called at [/home/xxx/core/Archive.php:801]
#23 Piwik\Archive->prepareArchive(...) called at [/home/xxx/core/Archive.php:614]
#24 Piwik\Archive->cacheArchiveIdsAfterLaunching(...) called at [/home/xxx/core/Archive.php:568]
#25 Piwik\Archive->getArchiveIds(...) called at [/home/xxx/core/Archive.php:508]
#26 Piwik\Archive->get(...) called at [/home/xxx/core/Archive.php:375]
#27 Piwik\Archive->getDataTable(...) called at [/home/xxx/core/Archive.php:470]
#28 Piwik\Archive::getDataTableFromArchive(...) called at [/home/xxx/plugins/Referrers/API.php:45]
#29 Piwik\Plugins\Referrers\API->getDataTable(...) called at [/home/xxx/plugins/Referrers/API.php:138]
#30 Piwik\Plugins\Referrers\API->getKeywords(...) called at [:]
#31 call_user_func_array(...) called at [/home/xxx/core/API/Proxy.php:211]
#32 Piwik\API\Proxy->call(...) called at [/home/xxx/core/API/Request.php:216]
#33 Piwik\API\Request->process(...) called at [/home/xxx/core/ViewDataTable/Request.php:48]
#34 Piwik\ViewDataTable\Request->loadDataTableFromAPI(...) called at [/home/xxx/core/Plugin/ViewDataTable.php:327]
#35 Piwik\Plugin\ViewDataTable->loadDataTableFromAPI(...) called at [/home/xxx/core/Plugin/Visualization.php:166]
#36 Piwik\Plugin\Visualization->buildView(...) called at [/home/xxx/core/Plugin/ViewDataTable.php:414]
#37 Piwik\Plugin\ViewDataTable->render(...) called at [/home/xxx/core/Plugin/Report.php:304]
#38 Piwik\Plugin\Report->render(...) called at [/home/xxx/plugins/CoreHome/Controller.php:78]
#39 Piwik\Plugins\CoreHome\Controller->renderReportWidget(...) called at [:]
#40 call_user_func_array(...) called at [/home/xxx/core/FrontController.php:577]
#41 Piwik\FrontController->doDispatch(...) called at [/home/xxx/core/FrontController.php:96]
#42 Piwik\FrontController->dispatch(...) called at [/home/xxx/core/dispatch.php:36]
#43 require_once(...) called at [/home/xxx/index.php:46]