[Crash] When i tried to close the window

When I tried to close the Ready to play window a message box with this:

System.ArgumentException: Item has already been added. Key in dictionary: '#rtp_cc_3429298'  Key being added: '#rtp_cc_3429298'
   at System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add)
   at System.Collections.Hashtable.Add(Object key, Object value)
   at System.Collections.Specialized.StringDictionary.Add(String key, String value)
   at Meebey.SmartIrc4net.IrcClient._StoreChannelsToRejoin()
   at Meebey.SmartIrc4net.IrcClient._OnDisconnected(Object sender, EventArgs e)
   at System.EventHandler.Invoke(Object sender, EventArgs e)
   at Meebey.SmartIrc4net.IrcConnection.Disconnect()
   at ReadyToPlay.Forms.ReadyToPlayWindow.CloseConnections()
   at ReadyToPlay.Forms.ReadyToPlayWindow.Window_Closing(Object sender, CancelEventArgs e)
   at System.Windows.Window.OnClosing(CancelEventArgs e)
   at System.Windows.Window.WmClose()
   at System.Windows.Window.WindowFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.PublicHooksFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)

popped up. Any reason for this?

EDIT: Just noticed update after posting; maybe that will fix it