compiled against non-compatible Arnold

If you see something like this:

[Arnold]: MAXtoA_Shaders.dll was compiled against non-compatible Arnold

it usually means you have an older Arnold trying to load something compiled with  a newer Arnold. There’s two common reasons for this happening:

  • The system PATH includes the location of the older Arnold, so the older Arnold is loaded instead of the Arnold version included with the plugin.
  • The plugin install is messed up, and has the wrong Arnold version in it.


[mtoa] Register failed for arnoldAOVChildSelector

If you see this error in the script editor

# Error: Register failed for arnoldAOVChildSelector #

that means your preferred render layer setup is Legacy Render Layers (so MtoA fails to register something that’s used for the new Render Setup).

If you’re not using Render Setup, then you can safely ignore this error.


[MtoA] Jittering color with user data

To jitter color with user data, you need to connect an aiUserDataInt to the data input parameter, like this:


The user data is an mtoa_constant attribute on the shape.  For example, if add an extra attribute named mtoa_constant_jitterID to some shapes, then you can use aiUserDataInt to read the jitterID.

If you want to use the shapes as standins, and be able to set the jitterID in the scene, then export the shapes without the mtoa_constant_jitterID attribute. In the scene, you’ll be able to add mtoa_constant_jitterID to the aiStandin node. The aiUserDataInt node in the ASS file will use that jitterID.

Buying Arnold



Annual subscriptions

You get annual subscriptions from Autodesk resellers

You can get Arnold 5-packs at 50% of the usual price, or you can get single Arnold licenses at full price:

Monthly subscriptions

  • You can subscribe for one, two, or three months.
  • Monthly Subscriptions are £60 / €70 / $65 Per Month
  • Monthly subscriptions are available online from

Permanent licenses

Until 30 April 2018, you can still get permanent Arnold licenses. Contact your local Autodesk reseller.

Arnold light_groups and shadow_groups

Light linking in Maya, include/exclude objects for lights in CINEMA 4D, light masks in Houdini, inclusive/exclusive lights in Softimage, they all are translated to light_groups and shadow_groups in Arnold.

Here’s a sphere on a plane, with two area lights (cyan and green).


If we add a light_group to the sphere polymesh:

 use_light_group on
 light_group "CyanAreaLight"

then we get this (see below). The sphere is lit only by the cyan area light: the light_group is the lights that affect the object.

Note that the sphere still casts shadows from the green light, even the sphere isn’t lit by the green light. That’s because there’s no shadow_group, so all lights cast shadows from the object.

If we add a shadow group, so that the light_group and shadow_group are both “CyanAreaLight”, then the sphere is lit by the cyan light only, and casts shadows from the cyan light only.

use_light_group on
 light_group "CyanAreaLight"
use_shadow_group on
 shadow_group "CyanAreaLight"


And finally, here’s the sphere when light groups are on, but there’s no lights in the light group:

use_light_group on
use_shadow_group on
 shadow_group "CyanAreaLight"


[OSX] Getting Arnold logs for batch renders

You can get individual log files for each frame:

  1. In the Arnold Render Settings, go to the Diagnostics tab.
  2. In the Verbosity Level list, click Warnings + Info.
  3. Click the File check box.
  4. Click the folder icon and choose a folder for the Arnold log files.


Or you can check the MayaRender log, which will be one log file, with the log messages for every frame.

On OSX, open the Console and look for ~/Library/Logs/Maya/mayaRender.log