Several "fixes" are available.
Move the lens aperture ring to the minimum aperture point and the warning will probably disappear. There is probably a lock tab on the lens available to keep it there too. In this arrangement the aperture is adjusted with the thumb wheel.
In the custom settings menu you can choose to set aperture with the ring rather than the thumb wheel. In this arrangement the aperture ring is left unlocked and there is also normally no fEE warning.