Ok thank you, renedef, for your answer! Are you talking about swirling planes from the traffic pack or is your own plane that you fly yourself behaving erratically?
About a month ago I uninstalled all my FS X add ons and reinstalled FS X... I began reinstalling add ons and have now only ORBX Southern Alaska, Fly by Wifi (an Ipad application) and these extra planes running: the new Aerosoft Airbusses (A318-A319-A320-A321) and the IRIS Pro Training series Pilatus PC-9. I can't fly the PC-9 anymore: when I start a flight with it I get a plane that is rotating around like hell... The default Maule Orion sinks in the ground and does abnormal things now too, but sometimes it works ok. I recognize your error messages about the GPS engine. I get an GPS Engine error telling me that the flight plan will not be used if I created a flight plan and the plane is unflyable due to sinking in the ground after I end the flight. Also in the flight planner when I plan a flight from Bold to Palmer Mun (two airports close to one another in Alaska (in the Orbx region), most of the time the flight is shown on the map erraticaly as a flight above the North Sea beween England and Norway... I think we have the same problem or something that is similar, only since I uninstalled UT2 it might not be to blame and ORBX might be the only problem causer.
I'm going to uninstall my ORBX now or tomorrow, and I'll let you know what that gives...
Have you got any problems with the flight planner too?