this is going to be so freaking obvious, but it’s driving me crazy!
i want to Bake the Bump details into a normal map.
i keep getting “Bump map not activated”
no matter if i have an 8bit or 16bit Alpha selected
I am not exactly sure how to do what you are trying, but this may another detour solution:
http://www.zbrushcentral.com/zbc/showthread.php?t=55689
Wish I can see someone can answer your question though, so that I can join to learn something new to me…
I noticed ZB3.1 has Zmapper rev E
ZB2 is rev D
Current Non- workflow
1) import UV maped .obj
2) create 1024 x 1024 texture with dark grey color
3) Select bump material
4) subdivide mesh to 5
5) Projection Master: paint light grey to white details
6) export texture.psd
7) convert to 16 bit greyscale
8) Sub level 1
9) import into ZBrush 3.1 Alpha (texture map is also loaded)
10) Displacement Tab: intensity 1 (or whatever looks best in preview)
11) Zmapper: Tangent space for Organics (Interpolative for Mech)
12) 
*Bump map not activated
this workflow works in ZB2
Attachments
According to the following thread, this is a known issue that’s being looked at.
This thread talks about the suggested workaround. Which is basically to generate a displacement map from the second or third highest subdivision level.
Hope this helps…MG
…at least i KNOW it’s not something i was missing;)