Cannot edit Chief material in Photoshop

[cache]

Hi guys,

Not able to edit a material in photoshop.

From Ps6 I try to get into the program data reference file for one of the chief textures and it says that it cannot open because it is the wrong file type. I thought these were just .jpg????

What I am trying to do is crop the jpeg file for the composite slate roofing down to just a single tile. Then when I apply it to a 3D solid, I can just press stretch to fit and it will appear as a single slate tile. I figured the best way to crop the image was in photoshop, but I can't bring up the file there.

Please help!