I'm sorry, but I'm afraid there are no other explanations, other than something in your system that prevent it to run.
I've just tested now again, just to be sure, on a Vista 64 machine (a Mac booting in Windows, on top of that...), with 6GB AND with FS9.EXE patched to use >2GB.
No problems whatsoever, FS9 runs at the first try, I've only installed KFLL, but that comes with same bglman files you have. Patching or not FS9 for >2GB with CFF explorer doesn't make any difference: it works in both cases.
And yes, I also have AVG installed with the latest A/V definitions just downloaded, and it's not even disabled.
BTW, KFLL is running at 70 fps in this setup...