I just created a MediaWiki (v1.26) to use PlantUML extension.
I followed all the installation steps, but when a add "require_once('extensions/PlantUML/PlantUML.php');" line to LocalSettings.php, my wiki main page changes to PlantUML.php.
I already tried to change it to: wfLoadExtension( 'PlantUML' ); - but wiki stops working.