Wordpress MultiSite Setup, and infinite admin loop for new site

OK so I am trying to set up my first Multisite and I am feeling like a total moron and out of my depth.

I got it setup on the main install - http://cloakinvestigations.com.au and I added the new site, parked the domain and it shows up - http://employmentscreeningaustralia.com.au My issue is if I go to the network admin and try to to visit the dashboard for the new site I get an infinite loop for the admin login. It just goes round and round and will not proceed to the admin. I have checked that the user has access to that site from the network admin.

Sorry for the idiotic questions, but I have been stuck for hours trying to figure it out.
All help would be much appreciated.

Simon