in twig template
{{ render(controller('FOSUserBundle:SecurityController:login',{})) }}
An exception has been thrown during the rendering of a template ("The
_controller value "FOSUserBundle:SecurityController:login" maps to a "FOS\UserBundle\Controller\SecurityControllerController" class, but
this class was not found. Create this class or check the spelling of
the class and its namespace.")
Remove 'controller' from the render, like this :
{{ render(controller('FOSUserBundle:Security:login',{})) }}