SQL & PL/SQL :: Query Works In 10g But Not In 11g?

I have the query below that works absolutely fine in Oracle 10g but is not running in Oracle 11g. Couple of things I notices about this query.

1. If I remove the alias 'FACILITY_W_CODE' in the ORDER BY clause, query works fine in 11g. If I replace 'FACILITY_W_CODE' with the actual fields - 'F.SERVICE_AREA || F.DISTRICT_OFFICE || F.DO_GROUP || F.DO_SSC' even then it works fine.

2. If I remove the GROUP BY clause in the inside query but keep the alias 'FACILITY_W_CODE' in the outside ORDER BY clause, the query works fine.

I am not sure where the issue is, GROUP BY or the ALIAS. Also, the alias issue seems to be only where the alias is used for multiple fields.

SELECT F.SERVICE_AREA || F.DISTRICT_OFFICE || F.DO_GROUP || F.DO_SSC FACILITY_W_CODE, PF.FAC_TYPE FACILITY_TYPE, PF.FAC_IDENT LOCATION_IDENTIFIER, P.DISTRICT_CODE USER_W_CODE, P.EMAIL_ADDRESS, PF.CERTIFICATION_AUTHORITY, PF.CALLBACK_TECHNICIAN, PF.CALLBACK_ENVIRONMENTAL
FROM PEOPLE P
JOIN (
SELECT I_PF.ID, I_PF.FAC_TYPE, I_PF.FAC_IDENT,

[code]....