Need help diagosing strange rendering behavior

[3ddesign]

I received a Max 2012 Vray 2.2 interior model from one of my consultants that is behaving very strangely. If I open the file and render on a single machine it might take 16 minutes. If I close Max and open the file again it might take 19, or 13 or 18. And each time the render comes out with slight variations in color and brightness. Then if I open the file and render with DR, it takes over 2 hours to render and I get subtle dark patches. I've tried merging it into a blank file, I've checked materials for anything odd, all paths are OK, it has IES lights that I've swapped out with ones I know render fine. I've tried rendering on one machine and saving the IR and LC maps then rendering with DR but still get long render times and dark buckets. Other files render fine on my system. Has anyone experienced this and/or have some idea what I should try next?

Craig

[MoonDoggie]

I just figured out some crazy render problems I was having. I don't think they're related at all, but somewhere in my scene I had an "Autodesk_Material" applied to some splines and for some reason a material in my scene (VRayMtl) had "Use Irradiance Map" turned OFF. Once I replaced the Autodesk_Material and turned "Use Irradiance Map" on for all materials (using "VRay Material Control" script, thank you). My scene's render times went from 17hrs to 45m. Just some other things to check, though I'm 95% sure these aren't the problems you were having.