title: Uncaught TypeError: Cannot set property of null
body: <p>I keep on getting "Uncaught TypeError: Cannot set property of null" whenever my code hits the js code below to open a popup when clicked on a label on aspx page. Please help.</p>
  
  <pre><code>function openWindow(which) {
              //alert(which);
              //alert(document.getElementById('iframeClass').src);
              document.getElementById('iframeClass').src = 'ViewIovationResults.aspx?ordernumber=' + which;
  
              //alert(document.getElementById('iframeClass').src);
                  if (divMap.style["display"] == "none") {
                  divMap.style["display"] = "";
  
              }
          }
  
      &lt;tr&gt;
          &lt;td width="190"&gt;&lt;STRONG&gt;Order Number :&lt;/STRONG&gt;&lt;/td&gt;                                                                    &lt;td width="200"&gt;                                                                &lt;a  onclick="javascript:openWindow('&lt;%# DataBinder.Eval(Container.DataItem, "Order Number") %&gt;')"&gt;&lt;%# DataBinder.Eval(Container.DataItem, "Order Number") %&gt;&lt;/a&gt;                                                          &lt;/td&gt;
      &lt;/tr&gt;
  </code></pre>