Web Page:

<ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager_Settlement" runat="server">
</ajaxToolkit:ToolkitScriptManager>
<ajaxToolkit:AjaxFileUpload ID="AjaxFileUpload_Settlement"
ThrobberID="myThrobber"
ContextKeys="fred"
AllowedFileTypes="xls,xlsx"
MaximumNumberOfFiles="10"
OnUploadComplete="OnClientUploadComplete"
runat="server" />

Reference

Web.config

<system.web>

<httpHandlers>
<!-- Using CombineCriptsHandler.axd as path of handler -->

<add verb="*" path="CombineScriptsHandler.axd"

type="AjaxControlToolkit.CombineScriptsHandler,

AjaxControlToolkit" />
<add verb="*" path="AjaxFileUploadHandler.axd"
type="AjaxControlToolkit.AjaxFileUploadHandler,
AjaxControlToolkit"/>
</httpHandlers>

</system.web>

system.webServer> <modules runAllManagedModulesForAllRequests="true" /> <validation validateIntegratedModeConfiguration="false" /> <handlers> <!-- Using CombineCriptsHandler as name of handler --> <add name="CombineScriptsHandler" verb="*" path="CombineScriptsHandler.axd" type="AjaxControlToolkit.CombineScriptsHandler,AjaxControlToolkit" /> </handlers> </system.webServer>