C# Error CS1537 – The using alias ‘{0}’ appeared previously in this namespace

C# Error

CS1537 – The using alias ‘{0}’ appeared previously in this namespace

Reason for the Error & Solution

The using alias ‘alias’ appeared previously in this namespace

You defined a symbol twice as an alias for a namespace. A symbol can only be defined once.

The following sample generates CS1537:

// CS1537.cs  
namespace x  
{  
   using System;  
   using Object = System.Object;  
   using Object = System.Object;   // CS1537, delete this line to resolve  
   using System = System;  
}