Can't open copy buffer and other problems

Sometimes when I try to copy something (usually happens while using Office
2007, but not always - sometimes seems to start in explorer) I get an error
message saying that the copy buffer can't be opened. Once this happens, it is
impossible to copy anything and the paste options on menus are disabled. All
applications are affected, not just Office or whatever application in which I
first notice the problem.

In addition, if I keep working once this has happened then other things
don't work either. For instance, if I ask to make a new folder in explorer,
the new folder does not show up (and hence I am not given an opportunity to
name it) unless I use F5 to refresh the window. At that point I can see and
rename the new folder but the new name does not show until I refresh, and
sometimes if I doubleclick on the folder (to open it), I get an error message
that the folder does not exist. If I refresh again, the folder can be opened.
Once this sort of thing starts to happen there is no cure but to reboot.

This never happened for the first 8 months or so running Vista, but then,
following an upgrade at some point, this started happening. At first it
happened rarely, but now it is almost daily (perhaps 4-5 times per week).

Is anyone else experiencing similar problems? Is there a cure?

I've posted this here since explorer is involved too, so I suspect it to be
an OS problem, not just an Office 2007 problem.

Thanks,

Melissa