ZBrushCentral

Need help with exporting Normal maps from ZB. 3.5

I’ve exported this low poly model into ZBrush 3.5 and I’ve added some details without changing its shape.

Now I just need the use the normal map.

I clone the normal map to export it but nothing happens when I click the export button!

I’ve been doing hours of searching but I had no luck at all!

How do you export NM Map in ZBrush 3.5?