Compiler Error CS1614

'name' is ambiguous; between 'attribute1' and 'attribute2'. use either '@attribute' or 'attributeAttribute'

The compiler has encountered an ambiguous attribute specification.

For convenience, the C# compiler allows you to specify ExampleAttribute as just [Example]. However, ambiguity arises if an attribute class named Example exists along with ExampleAttribute, because the compiler cannot tell if [Example] refers to the Example attribute or the ExampleAttribute attribute. To clarify, use [@Example] for the Example attribute and [ExampleAttribute] for ExampleAttribute.

The following sample generates CS1614:

// CS1614.cs  
using System;  

// Both of the following classes are valid attributes with valid  
// names (MySpecial and MySpecialAttribute). However, because the lookup  
// rules for attributes involves auto-appending the 'Attribute' suffix  
// to the identifier, these two attributes become ambiguous; that is,  
// if you specify MySpecial, the compiler can't tell if you want  
// MySpecial or MySpecialAttribute.  

public class MySpecial : Attribute {  
   public MySpecial() {}  
}  

public class MySpecialAttribute : Attribute {  
   public MySpecialAttribute() {}  
}  

class MakeAWarning {  
   [MySpecial()] // CS1614  
                 // Ambiguous: MySpecial or MySpecialAttribute?  
   public static void Main() {  
   }  

   [@MySpecial()] // This isn't ambiguous, it binds to the first attribute above.  
   public static void NoWarning() {  
   }  

   [MySpecialAttribute()] // This isn't ambiguous, it binds to the second attribute above.  
   public static void NoWarning2() {  
   }  

   [@MySpecialAttribute()] // This is also legal.  
   public static void NoWarning3() {  
   }  
}