airspeed problem in fs2004

Hello all - I'm trying to find the cause of the following problem that happens on several different a/c including the default lear and 777. Basically - the airspeed will suddenly drop to zero and a few seconds or minutes later will recover. This will happen several times through the course of the flight, generally at random.No, it is NOT the pitot heat but it reacts just like that except that turning the pitot heat on or off before or during the flight has no effect.The only add-ons I've updated are WxRE and FSUIPC( regged ).I'm trying to track down more specifics as to when and how it occurs but, so far, it seems random - happens in bad weather or clear weather. Ascending or descending.Has anyone run into this?Thanx,Vic Baron