Why can't I select a template makefile?

This question would be much easier with pictures, but why don't I always get the option of selecting my makefile for code generation? Usually, I select the box for generate makefile, and type the tmf file that I use to create a dynamic link library dll. For some reason, on one model, it just isn't there. No box, no selection, no place to add the makefile. All settings are the same, both are running in 2013b, but I don't have the same menu options in the code generation tab.