The message "Wrong Paper Size" will appear on your Brother machine's display if the paper you have loaded does not match the Paper Size setting programmed in your Brother machine or the driver settings, or if the paper is oriented incorrectly in the tray.
Loading the paper into the tray correctly
Paper should be loaded in the paper trays in portrait orientation. Do NOT load paper in the paper trays in landscape orientation.
Regardless of the paper size you are using, you must always load the paper into the paper tray so that the two longer edges of the paper face the left and right sides of the paper tray and the two shorter edges of the paper face the front and back of the paper tray.