How big are these tables?
How about changing AND SOURCE.TA_YEAR=2000 -> WHERE SOURCE.TA_YEAR=2000:

SELECT ;
CM.TA_EnrlID,;
CM.TA_PtntID,;
SUM(SOURCE.TA_PYMT) AS DrillItem ;
FROM ;
DRILLENRLTMP146897616_A CM LEFT OUTER JOIN TRANMASTERE1T1 SOURCE ;
ON CM.TA_ENRLID = SOURCE.TA_ENRLID ;
AND CM.TA_PTNTID = SOURCE.TA_PTNTID ;
AND CM.TA_YEAR = SOURCE.TA_YEAR ;
AND CM.TA_MONTH = SOURCE.TA_MONTH ;
AND CM.TA_PCPID = SOURCE.TA_PCPID ;
AND CM.TA_DEMOID = SOURCE.TA_DEMOID ;
Where SOURCE.TA_YEAR=2000 ;
AND SOURCE.TA_PCPTPID = 7 ;
AND SOURCE.TA_PCPID = 236 ;
GROUP BY ;
CM.TA_EnrlID,;
CM.TA_PtntID ;
INTO cursor sg1 nofilt