Hi, im quite new to Zbrush and one of my first test in Zbrush is a demon character, i played around and added som details and made a test displacemen map, but some how parts of the map are just grey and do not have the details i painted, 
hopefully the images can explain what im talking about, what im woundering about is, if its some kind of bug or it is me who have marked og masked somthing or turned some wrong setting on or somthing like that. Can anyone help me ?
This looks like a problem with the UV’s. What do you see when you press Tool>Texture>Uv Check?
ok, i will try and chek that as soon as i get home from work : )
Update ; i checked in maya, and it was 2 face whos uv´s had gone bad! and therefor overlaped a big part of the other uv´s. I have fixed the overlapping uv´s in maya, can i then use the stuff i have painted in zbrush in the first place ?.
It seems you are right, the uv check do show a red color on the parts missing from the displacement map. Here a picture of it and the uv layout and now for the million dollar question ; how do i fix it ? : )
Everything that is red is overlapping UV’s. I suspect that when you created the UV mapping, some parts of it went outside the 0,0 through 1,1 UV space. The result is that you get overlap. You were actually lucky to be able to create a displacement map at all! Normally, the computer rebels when you try to write two different values to the same texture pixel, with the result being that the program crashes.
There are three ways to fix your problem. One is to remap the model in your other program, being careful to keep everything in the 0,0 through 1,1 space. Another is to remap as above, but deliberately break things up into different spaces. You would then use Mutli Displacement 2 (part of Displacement Exporter) to create multiple maps; one for each UV space. The third option is to use ZBrush to remap the model. At level 1 you would assign a blank texture to the model (such as 2048x2048 or 4096x4096) and then press Tool>Texture>GUVTiles. You can now create a displacement map without problem.
Ok, thanks a lot, i will try that out !