Main Page: button :Convert DS9 Regions -> Ginga" is grayed out

Why the button on the right "Convert DS9 Regions -> Ginga" grayed out? If I have a valid Region file and a valid WCS, it should be possible to load on whatever we have on the ginger viewer the slit pattern. 
In general, it would be good to understand how this type of instruction works:
   self.check_widgets[b] = [("valid_wcs", self.PAR), ("valid_file", self.loaded_reg_file_path)]
