In trying to debug various strange issues on a machine, I found something strange - when I go to C:\Users\administrator and get properties, security tab, it lists the users (the local admin account, system, and 'administrator' which is the domain administrator account).

It all looks fine in terms of permissions (full control, etc.) compared to other machines. The one difference is there is a small red circle with an X to the left of the user icon/name.

Additionally, there are various folders where it says access denied under there - for example, my documents!

Even logged in as the local machine administrator account (which is not named administrator), I am unable to change the permissions - it says access denied.

Any ideas what this means and how to fix it? I even tried re-joining the machine to the domain.