Compiler Warning (level 3) CS0105

The using directive for 'namespace' appeared previously in this namespace

A namespace, which should only be declared once, was declared more than once; remove all duplicate namespace declarations.

The following sample generates CS0105:

// CS0105.cs
// compile with: /W:3
using System;
using System;   // CS0105

public class a
{
   public static void Main()
   {
   }
}