Q4. Sometimes i cannot manipulate the model by the mouse; When i try to rotate the model, only the specification tree will move. Why?

• Most possibly, you are activating the specification tree. When you click the white lines of the tree, the tree will be selected and the model will become dim. At that time, all the manipulations by mouse, such as zooming & panning, only affect the tree, but not the model.  To deselect the tree, click any white lines of the tree again.