Now I have not ever used MVVM Light Messenger, but as with any event aggregator/message bus, it makes sense so that the handler method takes in the object that it handles as an argument:
I have checked the source code and the registration looks as follows:
public virtual void Register<TMessage>(object recipient, Action<TMessage> action)
With that in mind, this definition:
private void HandleClearSettings(ClearNewProjectSettingsMessage message)
{
}
should fix your registration:
Messenger.Default.Register<ClearNewProjectSettingsMessage>(this, HandleClearSettings);