Suddenly getting 1 - 1.6 fps..??

Hi all..I was doing my vatsim flight from Munich to Amsterdam and despite the real weather option gave me a grey and rainy weather in Munich I was able to get fps's 13-16 (Locked 20). After I climbed above the clouds I got my "normals" between 17 and 20. All was going well until I reached the Dutch area... my frames suddenly dropped to 1.0 and stayed between 1.0 and 1.9 for 15 minutes which resulted me shutting down the sim. I had only the normal programmes (SBRelay, SB and ServInfo running). OK, I have experienced drops in frames sometimes even to, say, 5 - 10 in high detail airports, but this was sth special... There was some clouds, but nothing different from my previous flights/weathers.What the **** is going on with this simulator or my computer?My specs:xp1700+512mb40gbradeon 9600 with Omega driverswin2000Anyone seen frame rates like this appearing suddenly?Petteri