register forwards to blogs/create which gives 404 error to non-logged-in users

Fresh Multisite/BP install, several plugins installed, BlogsMU child theme.

I set up all the page templates for Buddypress forms like register, activate etc. These sites are accessible when I am logged in, but not as a logged-out user.

When I go to wp-login.php the "register" link under the form redirects to blogs/create - which gives me a 404 ("Sorry, we can't find the content you're looking for at this URL.")

Checked all the user related settings and the users are allowed to create accounts and blogs.

I even found a thread where somebody put the register.php into the child-theme folder and did that with no success.

Anybody with an idea? I can't get rid of the feeling that it is related to another plugin or that I am missing something really basic here...

Thanks in advance!