Thanks for your reply.
unfortunately the toipic was closed, so i am contcting you via email directly.
the hints you gave to solve the problem do not work for my website.
I deactivated all plugins, but the extra fields in the menu design do not show.
Also, it seems that my theme is using wp members for the login procedure and wp members seems to use the wp-login.php.
So this should be ok, but the forwarding does not work…
What can be done?