I've been working on a project- a ten story building. To make windows within the main solid of the builing, I've been subtracting the window solid from the main solid. I've had no problem up until this point. No matter what I do, I can not subtract any solids from the main building solid. Is there a cap on how much you can subtract? I've checked to make sure everything is planar. It is. But I can no longer subtract.