WCF::handleException() Unhandled exception: Class 'TeamSpeak3_Helper_String' not found

#0 /home/users/hellboard/www/wbb4/wcf/lib/data/teamspeak3viewer/TeamSpeak3_Framework/TeamSpeak3.php(315): TeamSpeak3_Helper_Uri->getScheme()
#1 /home/users/hellboard/www/wbb4/wcf/lib/data/teamspeak3viewer/TeamSpeak3Viewer.class.php(30): TeamSpeak3::factory()
#2 /home/users/hellboard/www/wbb4/wcf/lib/system/cache/builder/TeamSpeak3ViewerCacheBuilder.class.php(32): wcf\data\teamspeak3viewer\TeamSpeak3Viewer->connect()
#3 /home/users/hellboard/www/wbb4/wcf/lib/system/cache/builder/AbstractCacheBuilder.class.php(40): wcf\system\cache\builder\TeamSpeak3ViewerCacheBuilder->rebuild()
#4 /home/users/hellboard/www/wbb4/wcf/lib/page/TeamSpeak3ViewerPage.class.php(37): wcf\system\cache\builder\AbstractCacheBuilder->getData()
#5 /home/users/hellboard/www/wbb4/wcf/lib/page/AbstractPage.class.php(276): wcf\page\TeamSpeak3ViewerPage->assignVariables()
#6 /home/users/hellboard/www/wbb4/wcf/lib/page/AbstractPage.class.php(100): wcf\page\AbstractPage->show()
#7 /home/users/hellboard/www/wbb4/wcf/lib/system/request/Request.class.php(58): wcf\page\AbstractPage->__run()
#8 /home/users/hellboard/www/wbb4/wcf/lib/system/request/RequestHandler.class.php(139): wcf\system\request\Request->execute()
#9 /home/users/hellboard/www/wbb4/index.php(10): wcf\system\request\RequestHandler->handle()
#10 {main}