I've seen this not only with HIPS but with other McAfee products. Encapsulating all products under the McAfee Agent is a challenging task. The Agent is required to remain modular and dynamic allowing other McAfee products to interface all from a centralized UI. With the number of McAfee products doing this it's easy for blips to happen. Not to mention Windows has its own fair share of issues related to updating the notification window / systray. When this happens you can either manually execute mctray, call cmdagent.exe, or reboot the system.