Poor plan going from 10.2.0.4 to 11.2.0.2

Hi,

We have upgraded a database from 10.2.0.4 to 11.2.0.2 and moved from Windows to REHL6.

The following query runs very good in 10g but really poor (it has infact never finished) in 11g.

SELECT UOM,USER_NAME,ZONE_NAME,SUM (CUSTOMERS_LEFT) AS CUSTOMERS_LEFT,SUM (TIME_UNTIL_DONE) AS TIME_UNTIL_DONE,MAX (UPD)FROM ( (SELECT UOM,USER_NAME,ZONE_NAME,NULL AS CUSTOMERS_LEFT,NULL AS TIME_UNTIL_DONE,1 AS UPDFROM USER.LDX_KPI_PICKINGWHERE FROM_DT >= :B3 AND TO_DT <= :B2 AND KPIRESOLUTION_KEY = :B1)

UNION(SELECT UOM,USER_NAME,ZONE_NAME,CUSTOMERS_LEFT,TIME_UNTIL_DONE