The only reason I suspect that this is happening is that at some time the UAC was turned off and then turned back on...
If the pc is being used while the UAC is turned off any programs or utilitys used will get certain privilidges. If then however the UAC is turned back on certain utilitys and programs may not work as before. I've found through experience that you need to either keep it turned off or turned on all the time.

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