Fix "Validation (): Element xxxxx is not supported" problem in visual studio

We face common issue in visual studio "Validation (): Element xxxxx is not supported" for ASP controls.
To solve this issue follow below steps:

1. Close down Visual Studio 2008 or Visual Studio 2010.

2. Now make sure to show hidden files, folders, and drives. 
    To do so go to Folder Options -> then select the View tab.  

3. Now you need to go toh below path:
   My Computer >> [C:] >> Users >> [username] >> AppData >> Roaming >> Microsoft >> VisualStudio >> 9.0 / 10.0 (For VS 2010)  
   Or
   Users >> Classic .NET AppPool >> AppData >> Roaming >> Microsoft >> VisualStudio >> 9.0 / 10.0 (For VS 2010)  

4. Now delete all items in ReflectedSchemes folder. 

5. Restart visual studio and your problem will be solved.