ZAP = Zone Alarm Pro, yes? Assuming so, it's probably a conflict of softwares. Are you using McAfee's firewall as well, or is it just the stand alone AV product? If your Firewall and AV are separate, as long as you are certain that the update did come from McAfee, and that it's genuine, try disabling ZAPro before running the McAfee update, then reactivate ZAPro.