WORKAROUND RESOLUTION FOUND:
We looked at Lee’s installation and we could replicate the issue. We noticed however that by navigating directly to a deeper link within the admin system, that we were in fact logged in.
It’s as if we are authenticating and even though correctly authenticated we are being redirected to the no access page, if we navigate to http://whatever/wp-admin/options-general.php we are then redirected to login page, then when we login we succesfully go to dashboard and issue vanishes.
The workaround was to put a redirect in the .htaccess file which looked like
Rewrite Rule /wp-admin -> /wp-admin/options-general.php
