Looks like it's at the default of 2. OK, so after changing this to 8 and trying again, I got a new error. Something about the Scene Bounding Box Being Too Large. So I checked the scene scale. All good. Then I selected all objects and hit the letter O. This will zoom the view to include all objects in your current selection. Curiously, everything disappeared. Long story short, I repeated this process, but only selecting one group of objects at a time. Everything worked until I hit one object, the Main Walls, then everything disappeared again. Progress. I had modified this object the other day. So I selected all the point and hit Optimize. Now when I hit O, boom. Back to normal and I can see the objects again.
Now it renders again! Yahoo! Your tip got me in the right direction.
Now I need to learn more about the pixel size setting and, aside from RAM usage, why I would need to adjust it. Would it render faster? I know there is probably a loss of detail at some point.