We are using Umbraco v6.1.1 (Assembly version: 1.0.4902.15214).

I created a usercontrol with an ajax ModalPopupExtender. When I created the macro and pointed it to the usercontrol I got errors. So I removed the reference to the AjaxToolKit dll and used  

Assembly="Umbraco.Forms.References" Namespace="AjaxControlToolkit" TagPrefix="asp"

In the same VS2013 project, I created a different usercontrol also referencing the Umbraco.Forms.References.dll. This time I need to add an ajax TabContainer. As soon as I place this on the page, the design view displays an error:

Error Creating Control - TabContainer1[A]AjaxControlToolkit.TabContainer cannot be cast to [B]AjaxControlToolkit.TabContainer. Type A originates from 'Umbraco.Forms.References, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=null' in the context 'LoadNeither' at location 'C:\Users\GorbunN\AppData\Local\Microsoft\VisualStudio\11.0\ProjectAssemblies\jzhslysd01\Umbraco.Forms.References.dll'. Type B originates from 'AjaxControlToolkit, Version=4.1.7.1005, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e' in the context 'LoadNeither' at location 'C:\Users\GorbunN\AppData\Local\Microsoft\VisualStudio\11.0\ProjectAssemblies\p_43i_hy01\ajaxcontroltoolkit.dll'.

I removed the reference to Ajaxtoolkit dll from my project. Does Umbraco.Forms.References.dll contain the TabContainer control? How can I get this to work ?

Thanks,
Ninel