Problem with Query

Dear Experts,

I'm trying to develop query based report, facing issues with query execution.

SELECT CONCAT(T6.[BeginStr], '-',T0.[DocNum]) As 'Bill Entry No.', CONCAT(T6.[BeginStr], '-',T2.[DocNum]) As 'GRN No', T2.[DocDate] As 'GRN Date', CONCAT(T6.[BeginStr], '-',T4.[DocNum]) As 'PO No', T4.[DocDate] As 'PO Date', T0.[CardCode], T0.[CardName] As 'Supplier Name', CONCAT(T1.[ItemCode],'-', T1.[Dscription]) As 'Item Code-Name', T1.[Quantity], T1.[Price], T1.[U_Venspec] FROM OPCH T0  INNER JOIN PCH1 T1 ON T0.[DocEntry] = T1.[DocEntry], OPDN T2 INNER JOIN PDN1 T3 ON T2.[DocEntry] = T3.[DocEntry], OPOR T4 INNER JOIN POR1 T5 ON T4.[DocEntry] = T5.[DocEntry] INNER JOIN NNM1 T6 ON T0.[Series] = T6.[Series]

Getting error as "Sales order already selected in production order'"

Please help me