SAP Message USMD1506 - Mod./ent.&1, node ent.&2, hy.attr.fr.ref.&3: Refer.ent. &4 does not exist DOCUMENTATION USMD1506 : Mod./ent.&1, node ent.&2, hy.attr.fr.ref.&3: Refer.ent. &4 does not exist