OK... I renamed gamex86.dll in doom3/base, still the same error, so I uninstalled RoE, then Doom3, then deleted the Doom3 folder and reinstalled Doom3 without RoE, set it up and made sure it ran OK, patched it to 1.3.1.1304, and checked again it was still running OK. Next I copied DarkMod from the torrent into the Doom3 folder, and ran the DarkMod launcher. Again it ran first time, I changed the aspect ratio and screen resolution, and restarted. Once again it showed the Doom3 loading screen, then a black screen. This time there was one less warning in the console, with 160 warnings shown. It's a puzzle...