Hi, I have a sizable mesh ( about 141,000 polys ) , I think that, that is the problem-my mesh has no subdivisions, yet, pls. see attached screenshot, it is telling me to go to lowest subdivision,please tell me what I am doing wrong, thank you, CZ
Displacement and normal maps are by definition, difference maps. They are representations of the differences between your base mesh and your high resolution mesh.
When your mesh has no subdivision levels there are no differences to map out and therefore neither type of map can be created.
The whole point of a displacement map is to allow your low resolution model to render as if it has more details than it actually has. Without any differences, there is quite literally no need for a displacement map as the model already has all the details that the map would reproduce.
How did you create the model that you currently have?
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If it was an imported model that you have divided and at some point deleted the lower subdivision levels then you can most likely use the Reconstruct Subdivision Levels feature to get those levels back.
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If it was created in ZBrush and you have deleted subdivision levels you may be able to use Reconstruct to get the levels back.
Either way, once you have lower subdivision levels you can go down to them and use the Create Disp Map feature to generate a displacement map.
- If you have never subdivided the model then you most likely will not be able to use the Reconstruct feature. In this situation, a displacement map would be completely useless to you because your current model is the base mesh. You wouldn’t create a displacement map until you have subdivided the model and created high resolution details.
Given what you’ve written, I suspect that you might be trying to create a displacement map when in fact what you want is to create UV mapping. All types of maps that get applied to a model (color map, displacement map, normal map, diffuse map, specular map, etc.) are created based on the model’s UV’s. These UV’s can only be generated at the lowest subdivision level, meaning that this the only thing to do with mapping that you would normally do before dividing a model. UV mapping is created using the Tool >> UV Mapping sub-palette or the UV Master plugin.
Thank you for your reply, this is spot on, NOW I know what the “reconstruction” command is for, 
thanks-BTW, I was also under the impression, that the UVs are constantly updated as I go up in subdivisions? or did I understand incorrectly, from info posted line, then I paint, etc, Craig
Subdividing a mesh will alter the mesh at all levels of subdivision. This, in addition to performance considerations, is why it is better to work without UVs and create them after all your sculpting is done if your workflow allows you that luxury. If you create UVs for a low poly mesh, then subdivide that mesh, the lowest level of subdivision will no longer be exactly the same mesh you created the UVs for.
This is the reason for the storage of a morph target when working with existing UVs that have to be maintained. You store that MT for each subtool, switch to it when generating the maps, then switch back to the altered mesh before changing subdivision levels again, or the MT will be altered.
Thank you for your advice, as always, have nice weekend, Craig