Error 1 WebDataMenu1:Failed to create designer 'Infragistics.Web.UI.Design.DataMenuDesigner,Infragistics2.Web.Design.v9.1, Version=9.1.20091.2011, Culture=neutral, PublicKeyToken=7dd5c3163f2cd0cb' C:\Documents and Settings\Farhad\My Documents\Visual Studio 2005\WebSites\WebSite12\Default.aspx C:\...\WebSite12\
Dear Farhad,
The dll may has been removed from the GAC (General Assembly Cache). You could simply re-install the service release/patch (9.1.20091.2011).
Also, you need to create an AJAX-Enabled WebSite when using Infragistics AJAX controls such as WebDataMenu. When you're creating a new website, select ASP.NET AJAX-Enabled WebSite from the Visual Studio templates.
Regards,
Riana Subroto
Infragistics ASP.NET team