C# Error CS1681 – You cannot redefine the global extern alias

C# Error

CS1681 – You cannot redefine the global extern alias

Reason for the Error & Solution

You cannot redefine the global extern alias

The global alias is already defined to include all unaliased references and therefore cannot be redefined.

Example

The following sample generates CS1681.

// CS1681.cs  
// compile with: /reference:global=System.dll  
// CS1681 expected  
  
// try this instead: /reference:System.dll  
class A  
{  
   static void Main() {}  
}