There user isn't even authentication so probably not an issue with permissions, but just in case try logging in with a normal user.
So you have any custom authentication? Is forms based authentication enabled on your iis?
You can also try removing from role and trying to log in, making sure the base site is accessable without permission (as it could be that there is no place for the logged in user to go and it just keeps trying to find a place to redirect the user till it fails)