Import geht nicht

Stacktrace:

#0 /storagepool/c01021/htdocs/test.lrde.de/lib/system/event/EventHandler.class.php(252): wcf\system\event\listener\AbstractEventListener->execute(Object(wcf\data\user\group\UserGroupAction), 'wcf\\data\\user\\g...', 'finalizeAction', Array)
#1 /storagepool/c01021/htdocs/test.lrde.de/lib/data/AbstractDatabaseObjectAction.class.php(224): wcf\system\event\EventHandler->fireAction(Object(wcf\data\user\group\UserGroupAction), 'finalizeAction')
#2 /storagepool/c01021/htdocs/test.lrde.de/lib/system/importer/UserGroupImporter.class.php(42): wcf\data\AbstractDatabaseObjectAction->executeAction()
#3 /storagepool/c01021/htdocs/test.lrde.de/lib/system/exporter/WBB4xExporter.class.php(553): wcf\system\importer\UserGroupImporter->import(4, Array, Array)
#4 /storagepool/c01021/htdocs/test.lrde.de/lib/system/exporter/AbstractExporter.class.php(175): wcf\system\exporter\WBB4xExporter->exportUserGroups(0, 1000)
#5 /storagepool/c01021/htdocs/test.lrde.de/lib/system/worker/ImportWorker.class.php(141): wcf\system\exporter\AbstractExporter->exportData('com.woltlab.wcf...', 0)
#6 /storagepool/c01021/htdocs/test.lrde.de/lib/acp/action/WorkerProxyAction.class.php(104): wcf\system\worker\ImportWorker->execute()
#7 /storagepool/c01021/htdocs/test.lrde.de/lib/action/AbstractAction.class.php(53): wcf\acp\action\WorkerProxyAction->execute()
#8 /storagepool/c01021/htdocs/test.lrde.de/lib/action/AJAXInvokeAction.class.php(65): wcf\action\AbstractAction->__run()
#9 /storagepool/c01021/htdocs/test.lrde.de/lib/system/request/Request.class.php(89): wcf\action\AJAXInvokeAction->__run()
#10 /storagepool/c01021/htdocs/test.lrde.de/lib/system/request/RequestHandler.class.php(119): wcf\system\request\Request->execute()
#11 /storagepool/c01021/htdocs/test.lrde.de/acp/index.php(11): wcf\system\request\RequestHandler->handle('wcf', true)
#12 {main}