Measurement Preferences

Help! I have purchased Dorico and am trying to change my preferred unit of measurement to inches. However, the apply button is greyed out and won’t allow me to accomplish this. The other options are selectable. Any idea?

Do you possibly have a dialog box open in Dorico, or are you in the middle of editing a text frame?

No. I was in write mode. Pressed Cmd/Shift/L and opened dialog box then attempted to change. All other measurement options allowed me to press APPLY but that one. Weird.