I went to change a style setting in Properties/Appearance in XP SP3 and found that my previously working 'Windows Classic Style' theme was missing. When I tried to access the 'Advanced' button under the Appearance tab I get the error: "Error loading Visual Styles". I checked the service for Themes and it is running. I can access the Windows XP Style in appearances with no problem. The theme exists in the directory C:\WINDOWS\Resources\Themes.
I have searched the net high and low for a solution including Microsoft and can find nothing relating to a solution to this problem or its cause. How do I get my Classic Style back?