Meines Wissens verträgt sich ON und WHERE nicht.
Lass das WHERE einfach weg, dafür ein AND dazu:

SELECT
ALL A.VERTRT, A.KUNNUM, D.BZ1, D.PLZ, D.ORT, A.ORDNUM, A.BELNUM,
A.DRKDAT, B.ASTNUM, E."CHAR", E.ZF3, (B.POSWRT), B.GELMGE, E.VKPRS
FROM FSBD106/FSFAK00P A
LEFT OUTER JOIN FSBD106/FSFAK01P B
LEFT OUTER JOIN FSBD101/FSADR01P C
LEFT OUTER JOIN FSBD101/FSADR00P D
LEFT OUTER JOIN FSBD101/FSAST00P E
ON A.BELNUM = B.BELNUM
AND A.KUNNUM = C.MANNUM
AND C.ADRNUM = D.ADRNUM
AND B.ASTNUM = E.ASTNUM
AND A.DRKDAT BETWEEN &FDATE AND &TDATE
AND A.VERTRT = &VTX1
AND C.VWDART = 'VR'
AND C.ZNUM = 1
AND A.BELART = 'GD'
ORDER BY 001 ASC, 002 ASC

Gruß
Allrounder