Need Help.I execute one sql, but it sometimes can not work proprely( error code ORA-01791) and som

  oracle version: Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - 64bit Production

I execute one sql, but it sometimes  can not work proprely( error code ORA-01791)  and sometimes can give the right result.

sql:

select *  from (

select row_.*, rownum rownum_  from (
SELECT distinct t3.contentid
,nvl(f.count,0) count
,f.publishdate
,nvl(f.score,0) score
,nvl(f.rank,0) rank
,t3.parentcontentid
,t3.parentcontentitemid
FROM
 (
  SELECT distinct cc.contentid,c.parentcontentid,c.parentcontentitemid
  FROM t_e_content c ,t_e_catalog2content cc where cc.contentid = c.contentid
     AND cc.status = '0'
     AND (cc.catalogid
 in
    (
     SELECT catalogid
     FROM T_E_CATALOG ca CONNECT BY prior ca.CATALOGID = ca.PARENTCATALOGID START WITH ca.Parentcatalogid = 0