There is one particular orc npc in Chorrol who is totally transparent apart from the purple mesh where his head gear is missing. I assume meshes and textures of his clothes are missing. The question is how can I find out which meshes/textures are missing and should be replaced? I also have a problem with some npcs missing hands - you just see purple streaks. Again, how do I replace the correct textures? Thanks for all replies.

Invisible body parts (or anything that uses a texture, really) are a result of missing normal maps. Purple textures are a result of missing texture files (.dds). Download FormID Finder, and use it to determine what is missing, and from what mod, and where the resources should be located.

OK, thanks. I will try that tool. I hope it is easy to use.

It is. Very easy.