I have a vast collection of mods, mostly consiting of additions I've collected from the modding community and placed into a "MegaMod" for my own use.

Yesterday I attempted to put these into a single .bsa file, prepping beforehand with TES4FILES.

The bsa worked, but gave me some unexpected problems, forcing me to go with my old folder system.

Since this whole experiment, I've had some lasting problems with NPCs. Specifically, many of them have bright yellow faces. The meshes of their faces are still there and outlined, but there's no texture, just bright neon yellow.

I have several face mods installed (Ren, Tabaxi, etc.). I also have several custom races which I've used to facilitate these new faces and also add height, weight, etc. to actors.

Here's what I know so far.

-My main "MegaMod" esp shouldn't be the culprit, as I've installed backups from several days ago with the same yellow face issues.

-Not all NPCs have this problem. About 70%, however, are plagued, by my estimation.

-It's not effecting entire races, but certain NPCs within those races. For instance, one NPC from my custom race "RedguardRen" will have the yellow face while another won't.

-It seems to randomly effect both custom and Oblivion-vanilla NPCs.

-From my testing so far, the player's face seems to be unaffected.

-The bsa file which I created yesterday has been complely removed from the data folder.

-The texture paths for the custom faces still seem to be in order, still show the proper textures when opened in Nifskope, and nothing has changed in my mod's race menu.

- (EDIT) Also, NPCs with vanilla faces have also been effected by this.

Can someone please point me toward an angle/possibility which I haven't thought of yet?

UPDATE: Problem solved, fingers crossed.

Disabling all forty-three thousand of my mods and rechecking one by one, amazingly, showed the DLC Vile Lair to be the culprit. Apparently it had nothing to do with my failed .bsa experiment, which is strange since the problem only BEGAN after I tried compacting all those files.

Reinstalling Vile Lair from my trusty KOTN Downloadable Content Collection disk (that's right, Bethesda, I purchased each of these mods TWICE from you) solved the problem. I remain clueless about how an apparently corrupted DLC, with limited changes to the gameworld itself, would effect the textures on the faces of NPCs far and wide, including custom face textures and races not even touched by the DLC. Looking through the DLCVileLair file details in TESCS, no races are remotely touched by this mod.

If anyone would like to theorize about what might've gone wrong, I'm open for suggestions. By the way, the Vile Lair bsa was intact prior to my reinstallation, so I'm certain I didn't accidentally remove it while fumbling through the data folder yesterday.

This has to rank in my top 5 strangest experiences with modding Oblivion. Shame, too, because I'll probably be very skittish about messing around with bsa files from here on in, even though that may or may not have had anything to do with it.

Self-resolved (glad you got it sorted, and for posting information that may help others) and closed by request.