Can't assign random materials

I want to be able to randomly assign materials to my repeated generic model (in-place mass) and for some reason I get an error: “The parameter’s storage type is not a string.”

I attached a snip of the Dynamo.

Thank you!

Material parameters are stored with the material element. That’s why strings are invalid. You need to get the actual material elements and provide those.

I appreciate the fast reply @Nick_Boyts .