Just I drag and drop an asp.net controls on sharePoint page such as Web Part or SharePoint's Application.aspx page then I got the error "Element xxx is not a known element. This can occurs if there is a compilation error in Web Site, or the Web.config
file is missing." in SharePoint project.
But same is working fine on ASP.NET Project. I am using SharePoint 2010 and VS2010 Ultimate on Window Server 2008 R2.
I have uninstalled and installed both SharePoint 2010 and VS2010 but getting same error again.