How to resolve ORA-00902: invalid datatype

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Oracle

This is the query where i am getting error as ORA-00902: invalid datatype

SELECT mapg_id,
            tab_to_string (
               CAST (
                  COLLECT (
                        sourcetypes.stname
                     || ': '
                     || sources.sIdentifier) AS t_varchar2_tab),
               '',
               '; ')
               AS sources
       FROM sources, mapgroup_source, sourcetypes
      WHERE mapgroup_source.source_id = sources.source_id
            AND sourcetypes.sourcet_id = sources.sourcet_id
   GROUP BY mapg_id;

while same query is working perfectly in the another schema.