The issue here is that you are trying to make an AO pass the same way they do in Max. The huge difference is the Max workflow uses VRayLight Tex as the base image and we don't have that in VR for SU. 2 Solutions. 1- Just use the AO tick box in your GI settings and it will add the AO automatically (less flexible than having a separate pass.) 2- Remove your ceiling/roof and use pure white in your GI to flood the space with light. You'll have to test this one out. I have asked the Chaos guys to give us the VRayLightTex and the XtraTex pass in order to do AO the Max way, but for now this is what we have.

Hi again, Yes, I've got 64bit OS and SU, I use RT GPU CUDA for rendering. I've changed Dynamic Memory Limit to '0' and it helped a bit but I'm still not able to make more than 1920x1080px image. I've tried to render to VRimage and still the same problem. I turned of default displacement too. No idea what else can I fix. If you think there's any other solution, please help me.