Indesign cs4 update error

Hi,

We are working in Indesign cs4..i am getting error while updating the xml in Indesign cs4.but it is working fine in Indesign cs5.5 and cs6...i have added my script below,

function ReLink()

{

myDoc = app.activeDocument;

myLinks = myDoc.links;

for (j = myLinks.length - 1; j >= 0; j--)

{

                    myName = myLinks[j].filePath;

             var ext =  myName.substring(myName.length-3,myName.length) ;

           if (ext=="xml")

          { 

      var reLinkXMLFile = app.scriptArgs.get("reLinkXMLFile");

              var myXMLFile = File(reLinkXMLFile);

     myLinks[j].relink(myXMLFile);

     myLinks[j].update();

                    }

}

}

please someone help us to solve this problem.thanks in advance.