第一次在项目中用AJAX就受到严重打击 UpdatePanel+Timer

< asp:UpdatePanel  ID ="UpdatePanel1"  runat ="server" >
             < ContentTemplate >
                 < asp:Timer  ID ="Timer1"  runat ="server"  Interval ="60000"  OnTick ="Timer1_Tick" >
                 </ asp:Timer >
    < div  align ="left"  style ="FONT-SIZE: 10pt; COLOR: #ffffff" >
         &nbsp;
        结束时间： < asp:Label  ID ="Label_1"  runat ="server"  Font-Bold ="False" ></ asp:Label >
        当前时间： < asp:Label  ID ="Label_2"  runat ="server"  Font-Bold ="False" ></ asp:Label >
    </ div >  
            </ ContentTemplate >
</ asp:UpdatePanel >

为什么页面不时会弹下面的提示框出来。。。。。这么简单的控件都这样，受打击。

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Microsoft Internet Explorer
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Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 12031
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确定  
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