3Essentials supports the Mircrosoft ASP.NET AJAX initiative as follows:

• Shared Hosting:
  • Microsoft ASP.net 2.0 AJAX  Extensions 1.0 are installed on all servers which have ASP.NET 2.0. 
    • For information on whether your server/hosting plan supports ASP.net 2.0, see this article: What ASP.net versions (1.1, 2.0, 3.5) does 3Essentials support, and how do I enable/change versions?.  If your server/hosting plan does not support this feature, and you'd like to upgrade to a current plan version which does, please submit a support request to this effect.
    • Note, use of the AJAX Extensions requires certain items in your ASP.net web.config file for necessary assemblies, httpHandlers, httpModules, etc, to properly support use of  the extensions.  The attached sample code contains:
      • a web.config file with these entries
      • a sample asp.net page which utilizes the AJAX Extensions.
      • Important note: make sure the web.config for your application has the necessary entries (as included in our sample web.config) and that it's in the right location - your ASP.NET's application root.  Please see KB article Where does ASP.Net search for web.config file? for further clarification on this.
  • Microsoft ASP.net AJAX Library 3.5 (for ASP.net 3.5) is built into ASP.net 3.5, and therefore is supported on all 3Essentials servers which have ASP.net 3.5.
    • For information on whether your server/hosting plan supports ASP.net 3.5, see this article: What ASP.net versions (1.1, 2.0, 3.5) does 3Essentials support, and how do I enable/change versions?.  If your server/hosting plan does not support this feature, and you'd like to upgrade to a current plan version which does, please submit a support request to this effect.
• Dedicated server customers can request Microsoft ASP.NET 2.0 AJAX Extensions 1.0, or ASP.net 3.5 (with built-in AJAX 3.5) to be installed on their servers, if they wish; simply submit a support request this this effect.

The ASP.net AJAX Control Toolkit is supported on 3Essentials servers with corresponding .Net framework versions:

• ASP.net AJAX Control Toolkit 3.0.11119.0 is supported on .NET 3.5 Framework and Visual Studio 2008.  Toolkit version 3.0.11119.0 is only for users who are building on top of .NET Framework 3.5 using Visual Studio 2008.
• If you are using .NET Framework 2.0 and Visual Studio 2005 then you should use Toolkit version 1.0.11119.0.