SQL & PL/SQL

I am generating XML by use of DBMS_XMLGEN.getxml pakage and the output i am storing into one CLOB. Then i am reading the value from the CLOB by use of DBMS_LOB.READ for every 32767 count of data. Below is my code. My Total LOB length is 450755. In the loop, When it reaches 393205, i am getting the below error.

ORA-06502: PL/SQL: numeric or value error: character string buffer too small

DECLARE
    v_xml_clob     CLOB := EMPTY_CLOB();

    v_lob_length   INTEGER;
    v_index        INTEGER := 1;
    v_read_cnt     INTEGER;
    v_chunk        VARCHAR2(32767);

BEGIN
    o_ret_code := 0;

    SELECT  DBMS_XMLGEN.getxml ('SELECT OBJECT_NAME, OBJECT_TYPE FROM DBS_OBJECTS')
        INTO    v_xml_clob
        FROM    DUAL;

    v_lob_length  := NVL(DBMS_LOB.getlength(v_xml_clob),0);
    DBMS_OUTPUT.PUT_LINE('LOB Length : '||v_lob_length);

    v_index       := 1;

    -- Start to read the data from CLOB object
    WHILE v_index <= v_lob_length
    LOOP
        DBMS_OUTPUT.PUT_LINE('IN');
        v_read_cnt   := 32767;
        DBMS_LOB.read (
                    v_xml_clob,
                    v_read_cnt,
                    v_index,
                    v_chunk
                    );

        -- USe fnd_file.put function to place the XML data into concurrent view output
        fnd_file.put(fnd_file.output,v_chunk);
        DBMS_OUTPUT.PUT_LINE('v_index Start: '||v_index);
        v_index := v_index + v_read_cnt;
        DBMS_OUTPUT.PUT_LINE('v_index End: '||v_index);
    END LOOP;

EXCEPTION
WHEN OTHERS
THEN
    ROLLBACK;
    NULL;
END;

Please let me know what may be the problem

Thanks