InfoPath Dev

I am getting the below error whan trying to access a field on my form.

'XDocument.DOM.selectSingleNode(...)'is null or not an object File:script'js 

My namespace is set as...

XDocument.DOM.setProperty("SelectionNamespaces", 'xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2009-03-24T12:18:15" xmlns:dfs="http://schemas.microsoft.com/office/infopath/2003/dataFormSolution"');

 my code is...

XDocument.DOM.selectSingleNode( "/dfs:myFields/my:LastName" ).text = " ";

My Datasource looks like this...

myFields

   LastName

   FirstName

Does anyone see what I am doing wrong...I know it is a simple fix?

Catching this up to our email thread -- the namespaces are incorrect in the xpath. If you don't have IP 2007 with its wonderful Copy XPath capability, you can save your form as source files and look at template.xml in a text editor to see what the correct namespaces are for your xpath.