well, I tried the suggestion put forth and also changed the RPP upwards and there seemed to be no difference in the problem.  I thought it may be because of the combinations of the sky lighting and resolutions or one of those parameters alone so I changed each one in turn and rerendered , but unfortunately, no change. Frankly, I am at a loss to figure it out. You can see from the enclosed picture that changing the sky lighting had no effect on the problem. Aside from that or because of it, I would like to know the parameters some of you use successfully for your poly intensive scenes. Any suggestions will be greatly appreciated.