an unhandled exception of type 'system.stackoverflowexception' occurred

See more:

C#

WinForms

C#4.0

.NET4

public partial class EntryPass : Form
{
   public EntryPass()
   {
      InitializeComponent();
   }
   ActionForm af = new ActionForm();
   private void EntryPass_FormClosing(object sender, FormClosingEventArgs e)
   {
      bool cancel = true;
      if (MessageBox.Show("Do You Really Want to Quit?", "ExitWindow", MessageBoxButtons.YesNo, MessageBoxIcon.Warning) == DialogResult.Yes)
      {
         cancel = false;
         af.Activate();
         af.Show();            
      }
   e.Cancel = cancel;
}

I want that, when I close EntryPass form then it Activate the ActionForm (since it is already open). So for this I code as above, but when I run this code, I am getting this exception
"stackoverflowexception" in the line:

ActionForm af = new ActionForm();

Please help me...