https://userapps.support.sap.com/sap/support/knowledge/en/1915832
1915832 - ME21N : Runtime error SAPSQL_ARRAY_INSERT_DUPREC in subcontract PO - SAP ERP & SAP...
When trying to create Purchase Order (PO) with subcontracting item by T-code ME21N, you get runtime error SAPSQL_ARRAY_INSERT_DUPREC.