The correct answer is C) discharge relief valve leaking back to the suction side. In a properly functioning refrigeration system, the discharge pressure should be higher than the suction pressure. If the discharge relief valve is leaking back to the suction side, it would allow high-pressure refrigerant from the discharge side to flow back to the low-pressure suction side, resulting in both low discharge pressure and high suction pressure simultaneously. The other options are incorrect because: A) a fouled condenser would cause high discharge pressure and low suction pressure, B) improper superheat adjustment would affect suction pressure but not necessarily both pressures, and D) an overcharge of refrigerant would cause high discharge and suction pressures, not low discharge and high suction pressures.