Fatal error: Class 'Piwik_Plugin' not found in /home/artnet/public_html/stats/plugins/ExampleUI/ExampleUI.php on line 28

Fatal error: Uncaught exception 'Exception' with message 'The class ExampleUI couldn't be found in the file '/home/artnet/public_html/stats/plugins/ExampleUI/ExampleUI.php'' in /home/artnet/public_html/stats/core/Plugin/Manager.php:930 Stack trace: #0 /home/artnet/public_html/stats/core/Plugin/Manager.php(898): Piwik\Plugin\Manager->makePluginClass('ExampleUI') #1 /home/artnet/public_html/stats/core/Plugin/Manager.php(614): Piwik\Plugin\Manager->loadPlugin('ExampleUI') #2 /home/artnet/public_html/stats/plugins/CorePluginsAdmin/Controller.php(384): Piwik\Plugin\Manager->loadAllPluginsAndGetTheirInfo() #3 [internal function]: Piwik\Plugins\CorePluginsAdmin\Controller->safemode(Array) #4 /home/artnet/public_html/stats/core/FrontController.php(531): call_user_func_array(Array, Array) #5 /home/artnet/public_html/stats/core/FrontController.php(97): Piwik\FrontController->doDispatch('CorePluginsAdmi...', 'safemode', Array) #6 /home/artnet/public_html/stats/core/FrontController.php(184): Piwik\FrontController->dispatch('CorePlugi in /home/artnet/public_html/stats/core/Plugin/Manager.php on line 930