Every now and then (see examples when below), I'm getting
a Windows Installer dialog error message as follows:

"The feature you are trying to use is on a CD ROM or other
removable disk that is not available.

Insert the Microsoft Office XP Professional disk and Click
OK."

There's a Browse button.

As far as I know, there's never been Office XP
Professional installed on my PC.

It's looking for a file PRORET.MSI.

Examples of when this happens are when I right click on
Desktop icon or when I right click on a filename when in a
File | Open dialog.

Any ideas what do, other than trying to get hold of an
Office XP Professional disk? Any ideas why this is
happening?