Thanks also for the info. I figured it out, and it's a weird one... The Avenger's Female Armor mods in a particular combination create the GMST condition. They depend on the LeFemm official mod from Bethesda, and there's a dependency condition that hangs them up, since they were built with LeFemm 1.0 in mind, and the version that everybody uses is LeFemm 1.1 instead. Very strange.
Anyway, it looks like what I'll have to do is keep an archive of the Data Files directory so that I can always revert to a known-good condition of the game. I really should do this anyway, but now I have a motivation.
For the record? Grizzly's Female Guards works fine. Anybody wants the updated and patched ESM, let me know.
-KKC