WCF::handleException() Unhandled exception: Call to a member function canEnter() on null

#0 /usr/www/users/chevy001/forum4de/lib/system/user/activity/event/PostUserActivityEvent.class.php(55): wbb\data\post\Post->canRead()
#1 /usr/www/users/chevy001/wcf4de/lib/data/user/activity/event/ViewableUserActivityEventList.class.php(82): wbb\system\user\activity\event\PostUserActivityEvent->prepare(Array)
#2 /usr/www/users/chevy001/wcf4de/lib/system/dashboard/box/RecentActivityDashboardBox.class.php(60): wcf\data\user\activity\event\ViewableUserActivityEventList->readObjects()
#3 /usr/www/users/chevy001/wcf4de/lib/system/dashboard/DashboardHandler.class.php(71): wcf\system\dashboard\box\RecentActivityDashboardBox->init(Object(wcf\data\dashboard\box\DashboardBox), Object(wcf\page\DashboardPage))
#4 /usr/www/users/chevy001/wcf4de/lib/page/DashboardPage.class.php(52): wcf\system\dashboard\DashboardHandler->loadBoxes('com.woltlab.wcf...', Object(wcf\page\DashboardPage))
#5 /usr/www/users/chevy001/wcf4de/lib/page/AbstractPage.class.php(276): wcf\page\DashboardPage->assignVariables()
#6 /usr/www/users/chevy001/wcf4de/lib/page/AbstractPage.class.php(100): wcf\page\AbstractPage->show()
#7 /usr/www/users/chevy001/wcf4de/lib/system/request/Request.class.php(58): wcf\page\AbstractPage->__run()
#8 /usr/www/users/chevy001/wcf4de/lib/system/request/RequestHandler.class.php(139): wcf\system\request\Request->execute()
#9 /usr/www/users/chevy001/forum4de/index.php(10): wcf\system\request\RequestHandler->handle('wbb')
#10 {main}