The 3D View Error Warning is an exciting safety feature that we have added to APCC.  When you opened up the 3D View, APCC tied the celestial coordinates of the mount to the mechanical coordinates (gear angles) in the servo.   Celestial coordinates can be changed by user error, but the user does NOT have any way to change the mechanical coordinates, so they are very safe and stable.  APCC uses this relationship to verify that the celestial coordinates in the mount are reasonable.   If an error is made, and you calibrate on Vega when you are really pointing at Arcturus, APCC will detect this and warn you.

We debated how best to implement this safety feature, and the choice seemed obvious in short order.   Someone who is in the middle of an imaging run probably has numerous windows open.  Once a session is under way, we often minimize the APCC main window and the driver window to conserve desktop real estate.  However, many of us like to use the 3D View window as our "sanity check" on where the mount is pointing since it is a small unobtrusive window and is visual rather than numeric in nature.  The 3D View is often the only APCC window that we keep open all the time on our desktop.   Now, there is an even better reason to follow this approach!