I was wondering if you ever found a solution to this. My version of 2007 is having the same problem. Items with negative elevations do not plot. They plotted fine this morning on my check plots, but now refuse to plot on the finals. I checked all of these items as well, and same as you, I cannot select the items in the bad Viewport, but they are fine on the model space tab. All items are on the same layer, In fact, the only place where they plot correctly is in the irregular shapes viewport! Thx PJ