I worked for an ISP, and I can tell you that a sizable percentage of all incoming calls were the direct result of Norton antivirus borking things up... Especially the real-time email scanner, it is notirously bad for timing out in the middle of downloading your email.
Instant fix: switch to a different anti-virus program, and the problem magically goes away.
Instant fix: switch to a different anti-virus program, and the problem magically goes away.