I've been doing the same tute today, and have come across the same error message for the first time that I recall. Pretty easy to fix. 1) Go to Polygons->Cleanup[] 2) Reset the settings 3) Check "Nonmanifold Geometry" to on 4) Check "Faces With Zero Geometry Area" to on 5) Set Area Tolerance for zero geometry area. I had to play with #5 for a bit. Too much and half your model dissapears. Too little, and nothing hapens. I was using something like 0.001 (default = 0.0001) Note: Have a feeling that step 3 is unnecesary. Just so used to having to turn it on..