Thx. Makanyane. One of our coders has resolved this...

FYI

in bi\data\ui\ folder are 3 rsd files...named (save the extension) after the compositle files in the subfolders.

They do not regenerate if removed.

If strat3.rsd is deleted then the game still runs and references the strat_0x.tga files for each culture that has one in its ui\culture\interface\ folder.

The other 2 rsd files probably function similarly except their area of effect is different. It seems that rsd files do need deleting in order for certain effects to take place.