"user does not have access privileges"

[Richie]

Ok, here's the situation:
I use an external 3gig HDD as a "Briefcase" in
conjunction with WindowsXP Pro to backup my files and
occasionally xfer them between my laptop and desktop. It
generally works fine.

Occasionally, I've had problems opening up and
successfully synch-ing PDF files I've downloaded or made.
No big deal, right? I would just download or make them
again because I could not longer access the originals
myself (Access is denied says my computer, though I don't
know why). As a note, I am listed in the administrators
group and one of only two people to log onto my laptop
(where this has been occurring, and from which the
briefcase is based). I use the picture icon welcome page
because my wife likes it so using the Administrator login
has not been tried explicitly because I would have to
turn-off the fast-switching between users deal, which has
for the most part worked ok.

PDFs are recreateable so I wasn't too annoyed that the
only way I could delete these files before recreating
them was to go into the command line and manually delete
them.

But now, the son of a b* has started co-opting my Word
documents from which these replaceable PDFs are created
(it's not happening with just one file, by the way).

So, what is my computer doing? Do we need to seek some
sort of occultist? Why does it hate me?

Seriously, I'm fairly adept at navigating my way aroung
the software intricacies of XP Pro, so any help you can
provide me is greatly appreciated.

I've never heard of a virus doing this, and since my NAV
is continually updated, I doubt that's it.

Thanks in advance,
R