That's possible, although I'm pretty sure it happens whether ZoneAlarm is running or not. I uninstalled ZoneAlarm, and it still happened.

I did have a problem with ZoneAlarm Plus 3.0 and NAV clashing; even with ZA set not to check e-mail, periodically a ZA file would start using 100% of processor capacity, always when NAV was virus checking e-mail. That problem disappeared when I uninstalled ZA+ and went back to the free ZA 2.xx.