Hello guysi set up a a flight today. when i was on the ground and set up the FMC, i put Fl350 for CRZ, everything was good untill about Fl180 i check FMCand OPT ALT=Fl360 and MAX ALT = Fl404, if i remember correctly, so i changed the CRZ level to FL370, the suddenly had a message on FMC saying MAX ALT 293!!!! tried it second time 2 seconds later FMC message MAX ALT 335, tried it for 3rd time and it was all alright, changed FL350 to FL370...Any ideas guys?thanks very much in advance.

I don't have a specific answer for the FMC freaking out like that, but perhaps a "glitch" in the pressure/temp gradient in FS9? That could wreak havoc on your engine performance.