A glitch in the scenery or virtual mem issue?

A friend got this message while flying thru Brazil. Was wondering if anyone knows what causes these kinds of error messages,when he has 90 gig free on his HD. Wondering if his virtual memory needs increased,or if there are certain scenery in FS9 that have glitches. I myself was flying from KCLE to KRKS on autopilot in a HondaJet v4 and while sipping my coffee,the sim simply shut down and went to Desktop.But my problem doesn't concern me.The one for my friend does.Here is his error... "Your computer has run out of available memory.Flight Simulator will now exit.You may not have enough free space on your HD.Run disk cleanup..."yada yada. Hope someone has a solution. Thanks y'all.