Since using Vatsim I keep getting altitude problems. When I have reached my assigned altitude, atc tells me that I am 300 feet below my assigned altitude, when I correct this , atc then tells me I am 300 feet above my assigned altitude, so on my journey albeit a short one I am going up and down like a yo-yo. As far as I can tell, this happens with all my aircraft. I am running windows xp service pack2.
Your help would be most welcome.