Sadly, I too have had the same problem. I searched the boards here and see quite a few postings dealing with exactly the same issue. I have a feeling that Defraggler is not quite ready for the Vista environment. That is too bad as it is a good product that I have relied on for over a year. I suggest you try Auslogics defragger (see Cnet downloads). I ran it on my computer with a Vista 64 bit environment with no problem. It is also much faster than defraggler.