I always do manual upgrades.
I have admin_XXX.php and an admin folder. I just checked the includes/global.inc.php file andchanged the name of admin to admin_XXX, as per the file. It now works fine, thank you Strange that the upgrade didn't do this?
I spoke too soon!
I now get :
Security Alert: Possible Cross-Site Request Forgery (CSRF) or browser back button used.
when attempting to login.