Generate cmd line file throws an exception



If I check the Generate cmd line file, there is no textbox to set the location of the file, and when the Merge! button is pressed an exception is thrown:
System.InvalidCastException: La conversión especificada no es válida.
en ILMergeGui.DynaInvoke.GetProperty[T](DynaClassInfo ci, String PropName)
en ILMergeGui.DynaInvoke.GetProperty[T](String AssemblyName, String ClassName, String PropName, Object[] cArgs)
en ILMergeGui.Mainform.DoGenerateCmdLine()
en ILMergeGui.Mainform.btnMerge_Click(Object sender, EventArgs e)
en System.Windows.Forms.Control.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnClick(EventArgs e)
en System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
en System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
en System.Windows.Forms.Control.WndProc(Message& m)
en System.Windows.Forms.ButtonBase.WndProc(Message& m)
en System.Windows.Forms.Button.WndProc(Message& m)
en System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)