Update:
I have uninstalled and reinstalled the latest build. But the same issue is happening.
I have tested fresh installs with both Sub-domains and Sub-directories. Same issue. Once I have updated the wp-config.php and .htaccess files, you cannot log in to the site.
Even replacing with the old (working) wp-config.php and .htaccess files, the same issue occurs.
I have made sure mod_rewrite is active and installed.
Ahh, the joys of Alpha testing…