DO IF, ELSE: Else not being computed

Only the initial if statement variable computation is being completed--the ELSE part is being ignored. Can someone explain why? Many thanks.

DATASET ACTIVATE DataSet1. DO IF ((A1_SCN2_PR1_UE = 0 & A1_SCN3_PR1_UE = 0 & A1_SCN4_PR1_UE = 0 & A1_SCN5_PR1_UE = 0) | (A2_SCN2_PR1_UE = 0 & A2_SCN3_PR1_UE = 0 & A2_SCN4_PR1_UE = 0 & A2_SCN5_PR1_UE = 0) | (A3_SCN2_PR1_UE = 0 & A3_SCN3_PR1_UE = 0 & A3_SCN4_PR1_UE = 0 & A3_SCN5_PR1_UE = 0)). Compute FM_zero = 1. ELSE. Compute FM_zero = 0. End IF. EXECUTE.