as i found in this topic https://premium.wpmudev.org/forums/topic/disable-buddypress-registration i successfully disabled the Buddypress Registration and reactivated the wp-signup.php.
The problem is that the menu item "Website Creation" links to the buddypress website creation.
Here is the screen for your information what i mean.
Its the point "Erstellen Sie eine Website" or "Create a Website"
I think i somehow need to redirect this link
as example http://mydomain.com/websitedirectory/create/
to the wp-signup.php where it should end at the klick on that item.
Thanks in advance