The problem "rarely occurs" says the Vole, but might happen if you install a device driver, install a program, run a new program or remove a program.
So far the problem seems to be confined to Vista
machines, but if it starts happening to XP machines because of the WGA, be sure to let us know.
Here is the Volish note.
It is like walking through narrow corridors in Byzantium we are given to understand. But luckily we've never walked through narrow corridors in Byzantium. In the meantime, here's a pic of Al Gore a reader mocked up for a us a year or two back while you contemplate your Vista perambulation. µ