domain mapping and multi-domains single sign on


I am having some trouble with single sign on for my users in multisite. I have both domain mapping and multi-domains plugins installed and i would like a user to be able to sign in at (or and be automatically signed in on (or ie completely sync login cookies across all domains and subdomains in the multisite network.

I have enabled 'single sign on' in multi-site settings. I have also enabled 'cross domain auto-login' in domain mapping.

Although i am able to login to and automatically get logged into, it does not automatically log into or I hope that makes sense? Ie cookies are syncing to subdomains but not across top level domains. Is there something i am missing in trying to achieve this?

PS : I have tried with and without activating asynchronous autologin in multidomain plugin, it doesnt seem to change anything. I have also used a plugin called 'multisite user management' to ensure that all users do have at least a subscriber role on all sites.

Any help would be very greatly appreciated. I have opened support access to the site if it would be easier to take a look?

Thanks very much in advance