create or replace PROCEDURE GRANT_SELECT (schemaName in varchar2) AS

CURSOR ut_cur IS
  SELECT table_name FROM user_tables;

RetVal  NUMBER;
sCursor INT;
sqlstr  VARCHAR2(250);

BEGIN
  FOR ut_rec IN ut_cur
  LOOP
    sqlstr := 'GRANT SELECT ON '|| ut_rec.table_name
    || ' TO ' || schemaName;
    sCursor := dbms_sql.open_cursor;

    dbms_sql.parse(sCursor,sqlstr, dbms_sql.native);

    RetVal := dbms_sql.execute(sCursor); 
    dbms_sql.close_cursor(sCursor);
  END LOOP; 
END grant_select; 

ORA-25191: cannot reference overflow table of an index-organized table
ORA-06512: at "SYS.DBMS_SYS_SQL", line 909
ORA-06512: at "SYS.DBMS_SQL", line 39
ORA-06512: at "ACD.GRANT_SELECT", line 17
ORA-06512: at line 6

select ' grant all on '||owner||'.'||object_name||' to user_name;' from all_objects
where owner='username';

SQL> select distinct iot_type from dba_tables;
IOT_TYPE
------------

IOT_OVERFLOW
IOT