FS2002 Heading/Track Mismatch

On several occasions I have experienced that the aircraft heading and track suddenly goes offset by a large number of degrees. This seem to be happening on the Northern Hemisphere (I haven't checked on the Southern Hemisphere yet). Yesterday at the fix MAMED (N38 34.80 E057 42.00) we where two pilots flying online with the PSS B747 and we both came into the same trouble at this position, which made the FMC's unserviceable. The other pilot got an compass error of about plus 45 degress, and I got an error of about plus 115 degrees.Later I have checked on WSSS Singapore (our destination) offline and also with default aircraft and the same error occurs. We have both installed FSNavigator (latest version), and the navigation data there seem to be correct. We would appreciate help on this problem :-).Best regardsJan H. Sorensenhttp://www.jspanels.com/images/logo_small.gifHomepage: http://www.jspanels.com