The file griddef.xml contains the definition of the gridding for a project. It should be located into your "<Project name>DFLTS\Diagrams\" project directory. If the file for some reason could not be found, the system will try to load it from the "PDMSDFLTS\Diagrams\" location. If there is no file, the system will try to load it from the folder where the application executable file is located. The file in the executable folder should be delivered together with your Diagrams installation. If the file does not get loaded, an error message will be displayed in the console window (the Diagrams application additionally displays this information in the message log.)