Solution:

Add reference to WebDesktop.dll

Add the following in web.config:

In HttpHandlers:

      <add path="ISRes.axd" verb="GET" type="ISNet.WebUI.WebResourceHandler, ISNet.WebUI, Version=3.0.5000.1, Culture=neutral, PublicKeyToken=b1f2a8511635667a" validate="true"/>

In WebServer Handlers:

      <remove name="ISRes.axd_GET"/>

      <add name="ISRes.axd_GET" path="ISRes.axd" verb="GET" type="ISNet.WebUI.WebResourceHandler, ISNet.WebUI, Version=3.0.5000.1, Culture=neutral, PublicKeyToken=b1f2a8511635667a" preCondition="integratedMode"/>


That should be documented somewhere...

WebContextMenu is part of WebDesktop control. Yes, adding reference to WebDesktop assembly should fix the problem.

WebTextEditor has WebDesktopScriptDirectory property. This property gets or sets the IIS path to locate WebDesktop’s script directory. This property is only applicable when SmartWebResources is not enabled.

<WebUI:WebTextEditor ID="_Editor"
    ...
    ImagesDirectory="~/media/images/WebTextEditor/"
    ScriptDirectory="~/ExternalControls/Intersoft/WebTextEditor/"
    SharedScriptDirectory="~/ExternalControls/Intersoft/Shared/"
    WebDesktopScriptDirectory="~/ExternalControls/Intersoft/WebDesktop/"
    ...
</WebUI:WebTextEditor>

Hope this helps.