Xmldom.writeToClob error. [URGENT]

Question

Any idea why I get the following error when I call:
xmldom.writeToClob(root, xml_out);
ORA-20000: An internal error has occurred: CLOB to write to can not be null ORA-06512: at "XML.XMLDOM", line 37 ORA-06512: at "XML.XMLDOM", line 358 ORA-06512: at line 131
'xml_out' is initialised with null, but 'root' have some nodes and elements, but no text nodes. I do not get this error if I use
xmldom.writeToBuffer(root, v_xml);
Thanks
null

Answer 1

Thx for your response
the program looks like this:
I executed it from a Form;
PROCEDURE PRUEBA IS
xml clob;
vxml varchar2(100);
len integer := 1;
pos integer := 1;
f utl_file.file_type;
doc xmldom.DOMDocument;
ppal_node xmldom.DOMNode;
main_node xmldom.DOMNode;
root_node xmldom.DOMNode;
user_node xmldom.DOMNode;
tercer_node xmldom.DOMNode;
item_node xmldom.DOMNode;
ppal_elmt xmldom.DOMElement;
root_elmt xmldom.DOMElement;
item_elmt xmldom.DOMElement;
item_text xmldom.DOMText;
--Elementos de la cabecera
header_pi xmldom.DOMProcessingInstruction;
header_node xmldom.DOMNode;
CURSOR MODULOS IS
SELECT T_COAPI AS COAPI,
T_DNAPI AS DNAPI     
FROM     T
WHERE     T_COAPI = 'PES';
BEGIN
--Creamos un nuevo DOM document
doc := xmldom.newDOMDocument();
ppal_node := xmldom.makeNode(doc);
FOR Modulo IN Modulos LOOP
-- El nodo es cada modulo
root_elmt := xmldom.createElement(doc, 'Modulo');
root_node := xmldom.appendChild(main_node, xmldom.makeNode(root_elmt));
--COAPI
item_elmt := xmldom.createElement(doc, lit_COAPI);
item_node := xmldom.appendChild(root_node, xmldom.makeNode(item_elmt));
item_text := xmldom.createTextNode(doc, Modulo.COAPI);
item_node := xmldom.appendChild(item_node, xmldom.makeNode(item_text));
--DNAPI
item_elmt := xmldom.createElement(doc, lit_DNAPI);
item_node := xmldom.appendChild(root_node, xmldom.makeNode(item_elmt));
item_text := xmldom.createTextNode(doc, Modulo.DNAPI);
item_node := xmldom.appendChild(item_node, xmldom.makeNode(item_text));
END LOOP
f := utl_file.fopen('TEMP_DIR','PRUEBA.xml','w');
--Obtenemos la longitud del xml lob
len := dbms_lob.getlength(xml);
DBMS_LOB.CreateTemporary(xml,TRUE);
xmldom.writeToClob(doc,xml); -- HERE I GET THE ERROR
dbms_xmldom.WriteToFile(f,xml);
WHILE (pos < len) LOOP
vxml := dbms_lob.substr(xml,100,pos);
utl_file.put(f,vxml);
pos := pos+100;
END LOOP;
utl_file.fclose(f);
END;