Dear Fester,
I see your a local. I had to recalibate my 600 once I got it with the help from Tech support. All upload with Geo Mgr work fine as well as GSAK. If you still have the unit prepare to reset everything. From the map, click Right, Left, Right, Left with the joystick. A small box should pop up. Type in 21 for re-cailbrating the compass and 22 for the temp screen. Follow the instructions on the screen.
Let me know if this helps.