This issue is occuring on both my home and work computers, both using XP Professional and only running business applications. The home computer has the issue several times a week, the work computer has it several times a day. The work computer has also slowed down considerably in all activities from opening applications to opening and closing files.
The microsoft web site says it is an issue of open and unattended use of Outlook and brought about by downloading trial software, something I don't often do if ever and can't remember when I have done it last. I do not, however, routinely shut down either computer and do always have Outlook open.