Heading, Compass, RW and ND missmatch

Hi,during a flight with PSS A340 I ended up with a missmatch between RW direction and ND heading of about 40 degrees.Later on I had missmatch on several aircraft on several airports.Both with MS default Cessna as well as PSS A340 and freeware Beaver.I found lot of different tips to correct the error but nothing works for me. One tip was to do a complete reinstall, phu...After a while with deleted navdata, reinstall navadat with no succes,hacking in cfg-files suddenly everything was OK. But I can't find out which hack solved the problem. It seems to be a delay from the hack to the result.I just wonder, is there any general rule to follow when I get a missmacth like that in the navigation stuff??Some sort of checklist, do this, do this and do this and now its OK!/Jonny