Hello, I am both a beginner Blender and Armory user, so I apologize for my incredible noobdom.
I am trying to convert a blender file to work with armory, I assumed it wouldn’t work out of the box because of all the materials. I deleted all the materials, but I still can’t play the file, and I am stuck as to figure out why the file will not play.
The error message I get, you may see in the picture attatched.
Heyo @Skyfish!
Unfortunately there is a bug/regression in Build 11. If you spot an object with ‘empty’ material slot and delete that slot completely, the error should go away. This should also be fixed in upcoming Build 12.
Please let me know if that worked. There may be more issues still, happy to tackle that too!
I’m assuming it would have worked, were it not for that I now have a different problem: The play button vanishes when I open a saved file. It was there this morning, but now it is gone. I will try… turning it on and off again… and get back to you 
Oh I see, it was just swapping rendering enginge on launch, I got my play button back. Anyway, I have looked at every singel object in my file, there is probably about 100. But I found no empty materials. And all the materials I have are using armory PBR node. I don’t know how to find this empty material. I also tried with a default file (the cube) and it an error message as well, although it is a bit different.
I found the problem, a plant model I had downloaded and used, had leftover particle systems that, when deleted, I ceased getting the error messages.