Compiler Error CS0069
An event in an interface cannot have add or remove accessors
You cannot define an event's accessor functions in an interface. For more information, see Events (C# Programming Guide) and Interfaces (C# Programming Guide).
The following sample generates CS0069:
// CS0069.cs
// compile with: /target:library
public delegate void EventHandler();
public interface a
{
event EventHandler Click { remove {} } // CS0069
event EventHandler Click2; // OK
}