Validation (): Element "elementname" is not supported in ASP.NET WebForms in Visual Studio 2008 and Visual Studio 2005

Sometimes application will compile and run properly but in IDE you got following warning message on each control.

"Validation ():Element is not supported"

Solution:

Visual Studio 2008 - Delete all files from below location in your machine,

1:- C:\Documents and Settings\[Username]\Application Data\Microsoft\VisualStudio\9.0\ReflectedSchemas

2:- C:\Documents and Settings\[Username]\Application Data\Microsoft\VisualStudio\9.0\ReflectedTypeLibs

Visual Studio 2005 - Delete all files from below location in your machine,

1:- C:\Documents and Settings\[Username]\Application Data\Microsoft\VisualStudio\8.0\ReflectedSchemas

2:- C:\Documents and Settings\[Username]\Application Data\Microsoft\VisualStudio\8.0\ReflectedTypeLibs

Thanks