Ok, the good news is it looks like it should be easy to fix. For some reason Max isn't running the latest version with the patch.
Here's a direct link to the latest version:
http://emdesignviz.com/downloads/maxwell_light_lister.msJust to be sure, open it up in a text editor and it should say this about 5 lines from the top:
Code:
2012-04-16 | v1.1 | fixed bug with scanning the scene for multi-materials | EM
To be safe, delete the button you created before for the script in the Max UI, then run the latest script and recreate the button.
Hopefully that should fix it!