Hello
The Help module seems to be generating errors when the Block module is not installed.
After a fresh install of Drupal 8-dev and immediately uninstalling "Custom Block" and "Block" modules, the modules page (/admin/modules) is not accessible. Following error is shown:
Uncaught PHP Exception Symfony\Component\Routing\Exception\RouteNotFoundException: "Route "block.admin_display" does not exist." at .../drupal-8.0.x-dev/core/lib/Drupal/Core/Routing/RouteProvider.php line 127
Uninstalling Help (or reinstalling Block) module takes away the error.