Getting the Toolkit working with the VS 2008 web site designer [AJAX Control Toolkit 11119 release update!]
Since last week's release of the 11119 version of the AJAX Control Toolkit, some people have reported problems using the .NET 3.5 flavor of the Toolkit with the Visual Studio 2008 web designer. Our team has just updated the 3.5 ZIPs (AjaxControlToolkit-Framework3.5.zip and AjaxControlToolkit-Framework3.5-NoSource.zip) available from the 11119 release page to address the issue. Whereas the old assembly had version number 3.5.11119.*, the new assembly has version number 3.0.11119.*. This is the only change to the Toolkit and only the 3.5 version has been updated.
If you have already downloaded the 3.5 flavor of the Toolkit, please remove the Toolkit from your Toolbox (if present), download the new 3.5 ZIPs, extract the new files over top of the existing ones, and designer support should work as expected. We apologize for any inconvenience this may have caused.