Since I had been scratching my head over this for a couple of hours, and I could not find anything regarding this online, here it goes.
I was adding the RMA and RMA Product entities to the Field Service Mobile application in Woodford, but when I was attempting to publish the update, I received the subject error message.
Sure enough, looking at the entity fields, the statecode field is not selected, and there is no way to directly select the field.
To enable the Status field you need to enable the Status Reason field.
Hope this saves you from tearing out some of your hair :-).
(Woodford v12.1.1.44573 - your mileage may vary depending of version)