ajax 控件的有关问题.

ajax 控件的问题...........................................
我的网页上放一个ajax   ScriptManager控件
但调试的时候出现如下错误:
Microsoft   JScript   运行时错误:   'Sys '   未定义

并且在   Sys.WebForms.PageRequestManager._initialize( 'ScriptManager2 ',   document.getElementById( 'form1 '));   这一句时中段

请高手指点

------解决方案--------------------------------------------------------
在webconfig <system.web> </system.web> 里加上

<httpHandlers>
<remove verb= "* " path= "*.asmx "/>
<add verb= "* " path= "*.asmx " validate= "false " type= "System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 "/>
<add verb= "GET " path= "ScriptResource.axd " type= "System.Web.Handlers.ScriptResourceHandler " validate= "false "/>
</httpHandlers>
<compilation debug= "true ">
<assemblies>
<add assembly= "System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35 "/>
</assemblies>
</compilation>