DropDownlist and PageMethod

Hello,
I am using Master-Content Page  concept in my project and my ScriptManager is on masterpage. In my content page I am binding Branch Dropdown on page load and on the basis of branch selection I am binding my User DropDown. Though I could have used Cascading Dropdown for that but I chose PageMethod for it.
Following is the JavaScript in my contentpage:
        ///When Page completely loads add handler to Branch DropDownlist
                $(document).ready(function() {
                    debugger;
                    var ddlBranch = $get('<%= ddlBranch.ClientID %>');
         &nbs ...