[Mihnea Balta]

Multiple material assignment normally works, so I need more information about this:
- how are you trying to do it? (please describe the exact steps)
- what is the exact error message? Do you get that error message from Maya or from MXCL?
- do you see any other errors in the script editor?

Normally you right click the object and select "face" from the marking menu. Then you select the faces to which you want to apply the material and either right click and use the "assign new/existing material" menu options, or use "assign material to selection" in Hypershade, or drag the material with the middle button from Hypershade/Multilister onto the object.

[Mihnea Balta]

As the warning says, Maxwell does not support assigning multiple materials on instances. You can only have one material per instance, not several for each instance. It's not just a problem with Maxwell materials, it also shows up if you use the native nodes (lambert, phong etc.).

There are several ways to work around this:
- use copied objects instead of instances
- uncheck the "use instancing" box in the global render options
- split the object into several parts, so that each part has a single material; instance the parts separately after this.

The warning will still be shown if you instance an object with multiple materials and don't change the materials on the instances (e.g. a tree instanced many times in a scene). However, in that case the warning is harmless, as all the objects will render with the same material setup as the original, which was the original intention anyway.