As a long-time user of EnviroInsite you remember that the program used to stay in pan mode until you clicked the right mouse button. We changed that for a number of reasons. You have several alternatives:
(1) Use the scroll bars to move the view window
(2) Click on the middle mouse button and pan around the view while holding down the button. If you only have two buttons then you may need to go into your mouse driver software to get it to recognize a click to the mouse wheel as being the same as clicking on the middle mouse button.
(3) Click on the pan icon and pan multiple times (yes it can be annoying to do so)