Microsoft JScript runtime error: '__nonMSDOMBrowser' is undefined

Question

I'm working with a Webservice.
Whenever I use this webserivce the following exception has occurred!!! this exception doesn't concern to my WebApp files! it concerns to the WebService files.

Microsoft JScript runtime error: '__nonMSDOMBrowser' is undefined

The exception has occurred in the following function :

function WebForm_AutoFocus(focusId) 
{
  var targetControl;
  if (__nonMSDOMBrowser) {//Exception
    targetControl = document.getElementById(focusId);
  }
  else {
    targetControl = document.all[focusId];
  }
  var focused = targetControl;
  if (targetControl && (!WebForm_CanFocus(targetControl)) ) {
    focused = WebForm_FindFirstFocusableChild(targetControl);
  }
  if (focused) {
    try {
      focused.focus();
      if (__nonMSDOMBrowser) {
        focused.scrollIntoView(false);
      }
      if (window.__smartNav) {
        window.__smartNav.ae = focused.id;
      }
    }
    catch (e) {
    }
}

What's wrong with it ? Am I missing something ?