Weird issue, with no conclusion.
A single complete site was put it its own subdirectory, the made multisite.
After which the Main site admin is accessible, but network admin keeps loading infinitely.
Chrome says "This webpage has a redirect loop" and in
Firefox says 'The page isn't redirecting properly. Firefox has detected that the server is redirecting the request for this address in a way that will never complete.
This problem can sometimes be caused by disabling or refusing to accept cookies.'
But Cookies is Enabled.
Staff: please ask if u need site access info. rgds