It has to do with the code that is in wp-signup.php in lines 25 -33
if ( !is_multisite() ) {
wp_redirect( get_option( 'siteurl' ) . "/wp-login.php?action=register" );
die();
}
Wordpress doesnt allow signups on subsites. When someone tries to sign up on a sub site, it redirects them to the main site.
I am using the multi network plugin,
(https://wordpress.org/extend/plugins/wp-multi-network/)
even though a site may be the main site for an additional network, wordpress still sees it as being a subsite so it keeps redirecting in an endless loop. By commenting out those lines it fixed the problem.
Is there a way to make a plugin for this instead of having to hack core?
I found a conflict with Multi Network & Buddypress. When you activate buddypress on a new network, the title_ tags & toolbar displays the title of the main site from the original network. Is there a fix for this?