Issue using XMLAGG in package

Question

I have a query that works inside of Toad but I get an error when attempting to add it to an Oracle package. Any ideas of what the issue could be? We are running Oracle 10G fully patched.
The query is :
SELECT 1.xxx, 1.yyy, 1.zzz
, RTRIM
( xmlagg (xmlelement (c, 3.aaa || ',')
order by 3.aaa).extract ('//text()'), ',' ) AS List
FROM table1 1, table2 2, table3 3
WHERE 1.xxx = 2.xxx AND 2.aaa = 3.aaa
GROUP BY 1.xxx, 1.yyy, 1.zzz
Errors when trying to create the package:
PLS-00306: wrong number or types of arguments in call to 'XMLAGG'
PL/SQL: ORA-00904: "XMLAGG": invalid identifier
Thanks for helping

Answer 1

The package is 602 lines and the rest of it works. This works fine if from RTRIM to ProgList is removed or commented out.
Retrieve a Project Report                                                                               
     PROCEDURE READ_ProjectReport( oReasonCode OUT VARCHAR2, oMsgTxt OUT VARCHAR2, oReturnCode OUT PLS_INTEGER)
IS
     BEGIN
          oReturnCode :=0;
          oReasonCode :='00000';
          oMsgTxt :=' ';
          OPEN oReport FOR
               SELECT EP.PROJECT_NBR, EP.PROJECT_NM,
               , RTRIM
               ( xmlagg (xmlelement (c, SUBSTR(E.EMPLOYEE_NM, 1, 1),
     SUBSTR(E.EMPLOYEE_NM,INSTR(E.EMPLOYEE_NM, ' ') + 1 , 1) || ',')
               order by E.EMPLOYEE_NM).extract ('//text()'), ',' ) AS ProgList,
               EP.SCHEDULE_IMPLEMENTATION_PP
               FROM EMPLOYEE_PROJECT EP, EMPLOYEE E, ASSIGN_PROJECT AP
               WHERE EP.PROJECT_NBR = AP.PROJECT_NBR AND AP.USER_ID = E.USER_ID
               GROUP BY EP.PROJECT_NBR, EP.PROJECT_NM;          
     EXCEPTION
          WHEN OTHERS THEN
               oReturnCode := -1;
               oReasonCode := To_Char(SQLCODE);
               oMsgTxt:= 'ProjectReport:' || substr(SQLERRM, 1, 200);
               IF oReport%ISOPEN THEN
                    CLOSE oReport;
               END IF;          
END READ_ProjectReport;
Failed: 3 errors, 0 warnings
Line: 575, Column: 8
PLS-00306: wrong number or types of arguments in call to 'XMLAGG'
Line: 575, Column: 8
PL/SQL: ORA-00904: "XMLAGG": invalid identifier
Line: 573, Column: 4
PL/SQL: SQL Statement ignored
Hopefully this is more helpful.