It is unlikely that the PC is joined to a domain. What that would mean is that when you logged into the PC via the Windows Login, you would provide the domain as well as your login name so that the login could be verified against the domain credentials. If that server was not available, you would receive a warning that it was using a local cached profile for login.
So, to resolve your issue, can you go to Control Panel and click Automatic Updates and enable it there? If it *is* enabled, but OneCare thinks it isn't, try disabling it in Control Panel and then enabling it once again.
If this does not resolve it, please contact OneCare support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve