Tim Witort wrote:

Why would email scanning cause the error, but rebooting fix
the problem? Email is being scanned in both cases. The system
is using Norton Internet Security 2006, by the way. I will try
turning off email scanning to see if it helps, but something
tells me it is not the cause.

Somewhat off-topic, but I just heard today that there are big problems with
Norton 2006-series of products that can allow malicious code to run, even
through the firewall.
--
Brian Tillman [MVP-Outlook]