CRM 2013 soap retrieve Error:Unable to get property 'selectSingleNode' of undefined or null reference

Hi, 

For, retrieving records in CRM, I am using soap method by using js. I'm referring the below link for that.

http://vikramxrm.blogspot.in/2012/03/retrieve-multiple-records-using.html

But, it is giving me the error  "Error:Unable to get property 'selectSingleNode' of undefined or null reference" on below code line.

var errorCount = _ResultXML.selectNodes('//error').length;

I have also checked that it is not the IE version specific error.

Thanks,

Kandarp