find visible detail sides...bad detail brush side
Description:
The cause for this error is using multiple (incompatible) tool-textures on the same brush, or so it seems.
Apart from HINT and SKIP there aren't much combination of tool-textures allowed on the same brush, so any other combination is a possible cause. Tool-textures are the 'tools/' textures you can find using the texture browser in Hammer, and that have a special meaning.
Solution:
You will need to find the brush(es) with these tool-textures and replace those textures. The easiest way to find the source of the error is to hide all visgroups except for the visgroups which are for tools textures and then just look around the map in 3d textured mode.
See also:
WIKI: Tool textures
This error will cause your map to fail compiling completely