Right click the application when you start, and select "Run As Administrator" in the drop down. You may also do the same right click to go into the app's properties, and will be able to set "Always Run As Administrator" from there.
OK, I set up my ACAD "Properties", "compatibility" to "Run this program with Windows XP Service Pack 2" and to "open as administrator". I still get the compatibility error when I open Autocad but I can select "Run Program" in the error box and it opens. Is that normal to have to do that every time I open ACAD?