Hi Peter,
This works. Thanks again for your help.
SELECT distinct t0.[transid], T0.[CardCode], T0.[CardName], T0.[NumAtCard], T0.[DocDate], T0.[PaidToDate], T0.[DocTotal] - T0.[PaidToDate] as 'Balance', (select distinct max(t2.docdate) from orct t2 inner join rct2 t1 on t2.docentry=t1.docnum and t1.docentry= t0.docentry where t1.doctransid=t0.transid) as 'Last Payment Date' FROM OINV T0 inner join RCT2 T1 on t1.doctransid = t0.transid INNER JOIN ORCT T2 ON T1.[DocNum] = T2.[DocEntry] where t0.docstatus = 'O' and t0.installmnt > 1