I am using ajaxcontrols and in that all controls are working well But I had not found any of the control named as HtmlEditorExtender so I had just copied this tag in .html p
Try using ScriptManager instead of ToolkitScriptManager.
In my project, i'm also working with Editor control (ajax toolkit control) instead of HtmlEditorExtender. A Editor control do the same as the HtmlEditorExtender and you can have three panels Design Mode, HTML Mode and Preview Mode.
If you want to use Editor control instead just add the following register:
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit.HTMLEditor" TagPrefix="asp" %>
Hope it helps.
add <ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="Server" />
<%@ Register
Assembly="AjaxControlToolkit"
Namespace="AjaxControlToolkit.HTMLEditor"
TagPrefix="HTMLEditor" %>
add folowing tag in your web.config
<configuration>
<system.web>
<compilation debug="true" targetFramework="4.0" />
<pages>
<controls>
<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />
</controls>
</pages>
and in page
<ajaxToolkit:HtmlEditorExtender ID="replyBody_HtmlEditorExtender" runat="server" Enabled="True" OnImageUploadComplete="saveFile" ClientIDMode="AutoID" EnableSanitization="true" TargetControlID="replyBody">