I set up an ambient occlusion for mental ray render:

I picked mia_material_x_passes. Added mib_amb_occlusion nod to it on default settings, and finally applied the material to my objects. Now with the lights on everything works, but once I turn them off (and I have to, since I don't want shadows cast in my AO pass) everything is black.

I'm not supposed to need any light source for AO to work (at least I don't if I do it as render layer), but for a specific reason I have to have this AO rendered by MR. What am I doing wrong?

P.S.: I'm also not sure I render it correctly. Since I've already rendered the regular pass, I just render this as is... I don't uses passes in MR. I tested AO pass, just to see if it works but it doesn't.