Error: "missing } in XML expression"

Question

my date time picker JavaScript giving the following error ...please resolve my problem following is my code

// JavaScript File

function SetDate(dateValue) {
   // retrieve from the querystring the value of the Ctl param,
   // that is the name of the input control on the parent form
   // that the user want to set with the clicked date
   ctl = window.location.search.substr(1).substring(4);
   // set the value of that control with the passed date
   thisForm = window.opener.document.forms[0].elements[ctl].value = dateValue;
   // close this popup
   self.close();    
}

In Mozilla error console it gives the following error please have a glance on it.

Error: missing } in XML expression
Source File: http://localhost:1046/PlacementManager/Scripts/DatePicker.js Line: 8, Column: 57
Source Code: ctl = window.location.search.substr(1).substring(4);