I was flying IFR from LFPG to RJAA and at around The Netherlands, my Boeing 747-400 suddenly read that it was 3000 feet higher than it actually was. Control ordered me to descend... Then a few seconds later, they ordered me to climb because I was "20 thousand" below my assigned altitude o.O The error also registered in my cockpit, and the autopilot tried to correct the problem by climbing as quickly as it could (it made it up to 50000 before stalling and cracking the aircraft from stress). This happened both of the times that I tried to fly this flight in an ANA repaint of the POSKY B744. I was running at 4x Simulation. I'm still very confused.

Mayeb the pressure changed?but that wouldny explain a 20000 difference??????

The pressure wouldn't make a difference... if your altimeter is set to 29.92 above FL180, I'm assuming that the pressure doesn't change much above that altitude. I was at FL370 with clear skies below... I'm still going nuts over this though.

I've encountered that on occasion. It seems the weather downloader glitches on files sometimes. The pressure suddenly changes drastically, as if the numbers are way off. I've solved it by saving a mode and immediately re-downloading real weather. This seems to cure it as the bad files get replaced (hopefully).Lee