@rjbpa
Welcome to GPS Power. I moved your post to this existing thread.

You get that message when Updater is opened directly, i.e. it doesn't have a file loaded to it. You can either run it in Command Prompt and point it to the RGN file as suggested by the message, or run it conventionally by dragging an RGN file onto Updater.exe directly or its shortcut, e.g.:
Spoiler: Image
[Only registered and activated users can see links. ]

Select the appropriate radio button for "USB Device", connect the unit to be flashed in preboot mode and watch for its details to be populated in the window adjacent before clicking "OK".