Go to C:/Program Files/Firaxis Games/Sid Meier's Alpha Centauri. Open the file titled "Alpha Centauri" - the icon looks like a pad with a cog. In that file, replace "ForceOldVoxelAlgorithm=0" with "ForceOldVoxelAlgorithm=1". You'll still get an error message when you open AC, but then you can press Okay and it will work just fine.