Did you have more than one code for 502SU? The Maryland instructions specifically state that if you have only one code, you do not need to add form 502SU. "If only one of these subtractions applies to you, enter the amount and the code letter on line 13 of Form 502; then the use of Form 502SU may be optional." (page 7 at forms.marylandtaxes.gov/current_forms/resident_booklet.pdf )
