[DotNetDevelopment] problem in adding AjaxToolKit in ASP.NET 2005

[VB]

Hi,
I am unable to add AJAX Tool kit in my existing  ASP.NET 2.0
application.
I am getting below mentioned error when I am adding scriptManager and
updatepanel in my webpage from AJAXEXTENSTION toolbar. VS.NET 3.5
framework is also installed on my machine.

Microsoft JScript runtime error: 'Sys' is undefined

 Sys.WebForms.PageRequestManager._initialize('ScriptManager1',
document.getElementById('form1'));
Sys.WebForms.PageRequestManager.getInstance()._updateControls([], [],
[], 90);

please help..

Thanks,
VB