I didn´t test this code, but I think it should be

my.material = mat_flat;

I can´t say if the method works, there was once a very long thread about this issue, and it wasn´t really solved. Someone even tried to write a shader, but it didn´t work.
So I was surprised (and somewhat sceptical) about this very simple solution.
Anyway, I hope it works ...

That seemed to get rid of the error, thanks. Can't say that I see any difference with or without the effect when viewing the model with it in a test level. I guess I'll pursue this at a later date. Thank you for the help though.