creating materilized view with refresh on commit

Hello,

I'm trying to create a materialized view with refresh on commit. 

this works fine:

CREATE MATERIALIZED VIEW "EQUIPMENT_READINESS_SUM"
  REFRESH ON commit
  AS SELECT NVL(e.detached_master_unit_list_nbr,e.master_unit_list_number) unit_number,
    SUM(DECODE(e.equipment_status, '1', 1,0))  available
  FROM mls2_equipment_active e
  GROUP BY NVL(e.detached_master_unit_list_nbr,e.master_unit_list_number);

but If I tweak that calculation to:

CREATE MATERIALIZED VIEW "EQUIPMENT_READINESS_SUM"
  REFRESH ON commit
  AS SELECT NVL(e.detached_master_unit_list_nbr,e.master_unit_list_number) unit_number,
    SUM(DECODE(e.equipment_status, '1', 1,0))/100  available