selectsinglenode of namespace attribute

I'm loading an xml and doing selectSingleNode(//*[xpath])
xpath is with namespace attribute.

var xmlStr="<R AB:I='1' xmlns:AB='urn:MynameSpace'><I
xmlns:AB='urn:MynameSpace' AB:I='2'/></R>"

var abc=new ActiveXObject("MSXML2.DOMDocument.4.0");
abc.async=false
abc.loadXML(xmlStr)
abc.setProperty("SelectionLanguage", "XPath");
abc.setProperty("SelectionNamespaces", "xmlns:AB='urn:MynameSpace'");
alert(abc.documentElement.xml)//xmml i coming proper

DNode=abc.documentElement.selectSingleNode("//*[AB:I=2]");

alert(DNode)//this is coming as null


thanks,
praveen.


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