getting error

getting error

i am using jquery for popup 
the point is the same thing working fine on local server is giving error when i upload it to site 

the error are

"'.cannot call method click of null"

and

"
    1. Uncaught TypeError: Cannot call method 'click' of null
      1. (anonymous function) index.php:319
      2. jQuery.fn.extend.ready jquery-1.2.6.min.js:27
      3. jQuery.extend.ready.jQuery.readyList jquery-1.2.6.min.js:27
      4. jQuery.extend.each jquery-1.2.6.min.js:21
        "

        i am calling file like this 

        <script src="'.$theme['url'].'/js/jquery-1.2.6.min.js" type="text/javascript"></script> 
             <script src="http://techbits.co.in/forum/themes/default/popup.js" type="text/javascript"></script> 


        and popup.js is 
        "// JavaScript Document
        //SETTING UP OUR POPUP  
        //0 means disabled; 1 means enabled;  
        var popupStatus = 0;  
        //loading popup with jQuery magic!  
        function loadPopup(){  
        //loads popup only if it is disabled  
        if(popupStatus==0){  
        $("#backgroundPopup").css({  
        "opacity": "0.7"  
        });  
        $("#backgroundPopup").fadeIn("slow");  
        $("#popupContact").fadeIn("slow");  
        popupStatus = 1;  
        }  
        }  
        //disabling popup with jQuery magic!  
        function disablePopup(){  
        //disables popup only if it is enabled  
        if(popupStatus==1){  
        $("#backgroundPopup").fadeOut("slow");  
        $("#popupContact").fadeOut("slow");  
        popupStatus = 0;  
        }  
        }  
        //centering popup  
        function centerPopup(){  
        //request data for centering  
        var windowWidth = document.documentElement.clientWidth;  
        var windowHeight = document.documentElement.clientHeight;  
        var popupHeight = $("#popupContact").height();  
        var popupWidth = $("#popupContact").width();  
        //centering  
        $("#popupContact").css({  
        "position": "absolute",  
        "top": windowHeight/2-popupHeight/2,  
        "left": windowWidth/2-popupWidth/2  
        });  
        //only need force for IE6  
          
        $("#backgroundPopup").css({  
        "height": windowHeight  
        });  
          
        }  "


        i have echoed the popup in my php file like

        if($showlastpostmod)
        echo "<br/>";
        include 'man.php';
        echo '<br/><div id="popupContact">  
                  
                   </div>  
            <div id="backgroundPopup"></div><script type="text/javascript">
        $(document).ready(function(){  
        //LOADING POPUP  
        //Click the button event!  

        //CLOSING POPUP  
        //Click the x event!  
        //Click out event!  
        $("#backgroundPopup").click(function(){  
        disablePopup();  
        });  
         
        });  

        </script>  ';




        the i am frustrated because exactly the same thing is working ok on localhost.