Thanks again Michael ...
I left my office for a few hours with the computer on and the framing model hidden but still on. When I started to work again the problem recurred. Rebooting, as you suggested, fixed it.
But I found some other problems with the model itself. Solids that I had arrayed are now joined surfaces (except the parent one). Fortunately, for this project that is not really a problem. I don't know if these are related to the freeze phenomenon but it seems like unusual behavior.
I should note that this is a model that has been revised numerous times so sloppy changes on my part may be some of the cause (though not the display freeze).
cheers,
eric