Oh you got that problem. Oh that's just a simple icon mix up. That's a microsoft problem in that it allows only one program to share a file extention. Why. Who knows. Fix it by finding the extention in folder options just find the extention .mat and delete it. You don't need a registered extention with a material file. if you double click on a material like ya right the program is going to start up and show you the material like a picture? I don't think so.