Code module not setting up

backslash -> \Modules\YtVideos\Controllers\Admin_YtVideos::index

Thanks. It was stupid of me not to think of that. (I relied too much on the user guide where there is no backslash.)

The other problem I mentioned is that the module's Routes.php doesn't take effect even though it gets included. I can only set route definitions in the default Routes.php. What is wrong there?