OOM errors with Windows XP 64 bit? Why?

Hi, I have run windows xp64 for the past few months and FSX SP2 with various addon a/c. Yesterday I took out the PMDG MD11 for a 7 hour flight between EGLL and KPHL, and even though the OS is 64bit, I got the dreaded OOM error and FSX shut down.I did a return flight from KPHL to EGLL and on descent to EGLL there was some stuttering and then, the OOM dialog again.I am stumped as to why I'm getting OOM since my system is more than capable and it was fine during all kinds of long hauls in PMDG MD11 in the past. Has anyone with a 64 bit OS seen OOM errors resurface? I had them constantly when I was on xp32, but that is why I switched to xp64, and I don't know why it is now happening out of the blue. I thought it was darn near impossible to crash FSX with OOMs if you use a 64bit os.My system is tweaked according to NickN's instructions for both the Windows OS and FSX setup, and the drives defragged regularly with O&O. My system stats are below.Any advice?