Texture painting crash

I’ve been using a texture map to define wet areas on a mesh (so where to make the area appear wet) for meshes that don’t have enough vertices for vertex painting. It worked really well for me before but I’ve tried the process again, in a very similar fashion, I believe the only difference is I have multiple material slots this time. For example with this model of a river weir.

The problem is the second I click the engine to use the texture paint the engine immediately crashes to desktop.

Here’s my material set up, very simple, just using simple values for now.

As I’ve said I’ve done basically the same thing before in the same engine version with no issue. Is there something I’ve overlooked that I’ve done wrong or is this an issue with the engine? Any help anyone can give me is much appreciated

Okay, here’s an update, I re-imported the model with a single material slot and the texture painting is working fine. In the meantime I think I’ll have to paint the texture on another dummy mesh with one slot. I can carry the wetness texture over later on to the multiple material mesh.