I have The same Proplem! But My AI traffic is Also sinking in to The ground and atc continues to reminds Them to climb. When i load an aircraft after The flight plan My airplane sinks in to The ground and Then crashes. The only thing working propperly are The missions. Everything started when I installed GPWS For all My jets.
I Also have Windows 7, wich I know FSX is'nt made for, but everything had been working Great before. I have The acceleration expansion pack, World of AI traffic, GSX and some FSdreamteam airports. I have Also installed smaller texture files to get better performance. As I Said before I have some freeware GPWS installed.