The problem arose after SP1 in Vista Ultimate but then after SP2 it seemed to be corrected.
The fix back then was courtesy of Vad_M .......................................
adjust the UAC through Stardock Tweak Vista:
1. Press "Security" button. Then select the "Medium-low security" item in the "Overview" tab not the lowest setting as previous
2. Go to "Advanced" tab and select "Silently succeed" if you are an administrator and "Silently ignore" in the other case, do this even though the two appear to be mutually exclusive.
The item "Programs requesting elevation must be signed and verified" must to be unchecked!
You will never see the UAC message box after these simple tweaks. However all of DX options will work correctly.