You're posting to the
"microsoft.public.dotnet.framework.windowsforms.controls" newsgroup and so
that's why I assumed that this was an event attached to a custom
control/component. I just ran a quick test using code similar to the
following and it seemed to work as expected.

public class Form1 : System.Windows.Forms.Form
{
 ...

 private Connection connection;

 ...

 public Form1()
 {
   InitializeComponent();

   connection = new Connection();
   connection.MessageReceivedEvent += new
Connection.MarkReceivedMessege(connection_MessageReceivedEvent);
 }

 private void button1_Click(object sender, System.EventArgs e)
 {
   connection.FireEvent();
 }

 private void connection_MessageReceivedEvent(char ch)
 {
   MessageBox.Show(ch.ToString());
 }

 ...
}

public class Connection
{
 public delegate void MarkReceivedMessege(char ch);
 public event MarkReceivedMessege MessageReceivedEvent;

 public void FireEvent()
 {
   MessageReceivedEvent('A');
 }
}

And if I call the "FireEvent" method against the "connection" object, for
example through a Button Click event handler in the Form1 class, if fires ok
and a MessageBox is displayed with the string "A". Perhaps the exception is
somehow coming from a different line in the code?