Holey Socke

Years ago, to achieve a smooth look you subdivided if you didn't know any better. Then came playing with phong angles. I'm not sure how Blender deals with that, seems a bit complex from what I've read above. Other programs simply allow you to change the angle of vertex normals through a setting or tag and either apply it to the whole model or selected vertices/polys. If you're still having trouble getting a grasp on this CG Guerilla still have their much simplified explanation/tutorial videos on YouTube...and one specifically for this situation.

I find that some clothing designers, specifically those using Marvelous Designer are among the worst offenders through no fault of their own. MD generates high poly garments, much more so than needed for a game engine. Unfortunately, to keep using that program and still be poly friendly, a designer would have to learn how to retopo in a program they're unfamiliar with and that's likely not going to happen. I agree with a lot of the previous sentiments that items were imported into SL with little knowledge on the subject. A lot of full perm builder kits are just that, items brought in from other sources and not designed for SL....now people buy those kits and flood the grid adding to the poly count flood.

When you export through C4D you're given two versions of Collada to choose from. Use the 1.4 version as 1.5 is not compatible with SL. If the error continues, then there is a structural anomaly with your mesh that perhaps you need to look at. Hope this helps.