Baking normals problem

Hey guys
Baking normal maps is freaking me out again. I sculpted 2 objects with dynamic typology and made another low poly mesh for each sculpt. For the low poly mesh I also used a shrinkwrap modifier. I already tried to bake without any modifiers but the result is the same. The upper one looks alright when I use “world” or “object” for normal map baking and baking AO also works fine. On the lower ones every baking attemp causes artifacts. I already checked and recalculated the normals. Seems right to me. I also removed the doubles and I’m using smooth shading.
Do you have any idea what issue causes these artifacts?

After the last character I baked normal and AO maps for I thought I finally managed to do this but seems like I still don’t know every trick.

either your mesh has doubles ( select all in edit mode >> remove doubles ) or the normals are screwed up ( select all in edit mode >> ctrl N >> recalculate normals outside )