You probably have a magnet or metal on your desk near the compass. Make sure where place in near your computer is away from any metal objects or electronics like speakers.
Don't have it too close to the computer either. Use the USB cord and keep it a foot or two away.
I get the error when I have a screwdriver or pen near the landing leg. I even get the warning in the app when I land on my deck and happen to land close to a deck screw.
Compass error is only valid if you are in open space away from all metal objects.
When you calibrate the compass, take off all metal. No watches, no rings, not even keys in your pocket.