Can't select root network drive for duplicate file finder

I have several network drives mapped on my computer (Windows XP SP3, CCleaner 4.01.4093). I am unable to select the root drive letter to search for duplicate files. I can select subfolders, but, for example, I have a network drive mapped to S:\ and I can individually add all subfolders under S:\, but not S:\ itself which will make setting up a duplicate file search for this drive extremely tedious. If I go in to the registry and manually change one of the search entires to S:\, it will show in the search list but still will not search it.