SQL & PL/SQL

I have this XML

<?xml version="1.0" encoding="UTF-8"?>

<xfdf xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve">

<fields><field name="ATest1"><value>MGM Family</value></field>

<field name="ATestRNo"><value>46464647738</value></field>

<field name="IName"><value></value></field>

</fields>

</xfdf>

I write this:

Declare

    tagValue VARCHAR(100);

    xml      xmltype;

Begin

xml := xmltype.createxml(out_clob);

  SELECT EXTRACTVALUE ( xml, '//ATestRNo', 'xmlns="http://ns.adobe.com/xfdf/" xml:space="preserve"') INTO tagValue

  FROM dual;

  dbms_output.put_line ('EXTRACTVALUE = ' || tagValue );

end;

I run on SQL - DEVELOPER. I am getting this error:

ORA-31013: Invalid XPATH expression

ORA-06512: at "SQLOWNER", line 6

ORA-06512: at line 2

I expect output 46464647738.

Any pointers?