That doesn't sound like any Windows Mail error message I ever heard of.
Which antivirus or other third party security software are you running?
Some of them cause problems with Windows Mail over time. As a
minimum, email scanning in the antivirus should be turned off, although
that may not be sufficient to eliminate all of its bad effects.
Email scanning in any antivirus must be disabled, for reasons explained
here:
http://thundercloud.net/infoave/tutorials/email-scanning/index.htm
If turning off the email scanning function does not resolve your problem,
do a trial uninstall of your antivirus. If no improvement, you can
always reinstall it. Instead of uninstalling your antivirus, consider
upgrading to Windows Live Mail, because it is less prone to
suffering bad effects from overly aggressive antivirus programs.
http://download.live.com/wlmail