Okay people, it may be REALLY late (or early, depending on how you look at it), but it took me a LONG time to fix this - and besides it's useful info anyhow!
Anyway, all of us using UT's S3TC textures have experienced the 'black textures' problem where a specific texture has not been masked correctly.
It's an easy fix to implement, just replace the S3TC .utx file with it's 'normal' equivalent!
At least you can do this IF you know which ones to replace.
Here's the ones I found so far (took me F***ING AGES!)
-------------------------
Problem 1: Using Oldskool Ampd to play the 'original' Unreal levels in UT. The 'brown mountains' that are part of the horizon texture on Nyleve's Falls (level 2) are incorrectly masked.
Solution 1: Replace the S3TC 'skybox.utx' with the 'normal' skybox.utx from UT CD1.
-------------------------
Problem 2: In 'DM-Viridian-TOURNEY' there is a skybox area with incorrectly masked 'brown mountains with mist at the bottom'.
Solution 2: Replace the S3TC 'indus1.utx' with the 'normal' indus1.utx from UT CD1.
-------------------------
Problem 3: Using Oldskool Ampd to play Illhaven Saga, the 'moon with lower right shaded' on the illhaven level (level 2) is incorrectly masked
Solution 3: Replace the S3TC 'shanesky.utx' with the 'normal' shanesky.utx from UT CD1.
That's all I found for now...
If everyone using S3TC textures does these fixes on their systems and finds any MORE 'black textures', just post a screenshot, along with the level it came from and I'll see what I can find.
Better still, if YOU can find the fix for the 'black texture' you discovered, post a description of the problem and a solution to it as well!
Anyhow, enough for now!
I'm knackered and going to bed now!