hey,thanks for your reply,
now i solve this problem myself.whenever you got this type of error then please check your controls which you used in your code.
i use async file upload control.which increase loading time for java script.so i simply remove it and put simple file upload control as per below.
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<Triggers>
<asp:PostBackTrigger ControlID="btnUpload" />
</Triggers>
<ContentTemplate>
<ajaxtoolkit:asyncfileupload runat="server" id="AsyncFileUpload1" width="300px" UploaderStyle="Traditional"
uploadingbackcolor="#fff" clientidmode="AutoID"></ajaxtoolkit:asyncfileupload>
<br>
</br>
<asp:button runat="server" id="btnUpload" cssclass="btn btn-blue" onclick="btnUpload_Click"
text="Opslaan" />
<br>
</br>
</ContentTemplate>
</asp:UpdatePanel>
so now i get solution for my problem
Thanks!
ketan