From the error guide:
mixed face contents
Entity 0, Brush 12: mixed face contents
Texture ROCK_X1 and SKY
Entity 0, Brush 37: mixed face contents
Texture STEEL_9 and WATER7
In Halflife, brushes are required to have all faces be of the same type (solid, water, slime, sky, origin). Fortunately almost all textures are solid. If you put a water texture on one side of a brush which has dirt or steel textures for example, that would generate the error. The engine needs to know what is inside the brush, and it would be real confusing if different types could be put onto the same brush.
The fix is relatively simple. Simply find the offending brush, and then the faces with the inappropriate texture and change it. If a brush uses SKY, all sides must be sky. The same is true for CLIP, and ORIGIN textures as well. If you are careful it is possible to mix water textures (provided you don't accidently use a slime texture on the brush)
Bevel is located inside of ZHLT.wad file.
It is an texture whos purpose is to be read by the compiler and perform a special function.
Bevel removes the side on which it is applied from game. If you apply bevel to one side of a box, that side will no longer be visible/exist.
You have ZHLT.wad with ZHLT compile tools. Also, use the newest VHLT tools:https://sites.google.com/site/gshltools/compiler-tools