How to create duplicate allowed attributes

I'm using a custom attribute inherited from an attribute class. I'm using it like this:

[MyCustomAttribute("CONTROL")]
[MyCustomAttribute("ALT")]
[MyCustomAttribute("SHIFT")]
[MyCustomAttribute("D")]
public void setColor()
{

}

But the "Duplicate 'MyCustomAttribute' attribute" error is shown.
How can I create a duplicate allowed attribute?

Stick an AttributeUsage attribute onto your Attribute class (yep, that's mouthful) and set AllowMultiple to true:

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public sealed class MyCustomAttribute: Attribute

AttributeUsageAttribute ;-p

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class MyAttribute : Attribute
{}

Note, however, that if you are using ComponentModel (TypeDescriptor), it only supports one attribute instance (per attribute type) per member; raw reflection supports any number...