Situation: We are inputting Trimble signal into the 2600 for swath control on a 4830 sprayer- it has been working fine(about 1000 acres).  Recently it has stopped documenting(painting the map) for the reason of not valid gps.  The swath control pro is still working though- sections are shutting on and off for the most as they should.  The gps indicator on the screen shows a full green bar that says 3d Diff.  We are importing the signal from a Pro 600 display.  If I go in to the diagnostics on the 2600 it shows me the lat lon of the gps as well as corrections- and like I said the swath pro still works so what am I missing?  I had written all of the settings down when we initially set this unit up- and have checked and rechecked- with no success- I am looking for ideas on this one- is it possible that my GPS is not valid?  Why would I stop mapping if it is still receiving some sort of GPS?  Thanks for any input.