Help on Admin menu creation

Hi there!

Can anyone give me an hint on how this function is not working?

public function registerOptionsPage() {
if ( is_callable( array( $this, 'options_page' ) ) ) {
if( !empty( $this->_selfMainMenu ) && is_callable( array( $this, 'about_page' ) ) ) {
$this->menuHook = $this->_slug . '-home';
if(function_exists(add_object_page)) {
add_object_page( $this->_pageTitle, $this->_menuTitle, $this->_accessLevel, $this->menuHook , array( $this, 'about_page' ), plugin_dir_url( __FILE__ ) . '/' . $this->_appIconFile );
} else {
add_menu_page ( $this->_pageTitle, $this->_menuTitle, $this->_accessLevel, $this->menuHook , array( $this, 'about_page' ), plugin_dir_url( __FILE__ ) . '/' . $this->_appIconFile );
}
add_submenu_page( $this->menuHook, $this->_pageTitle . ' - Overview', 'Options', $this->_accessLevel, $this->menuHook . '-page', array( $this, 'options_page' ) );
add_submenu_page( $this->menuHook, 'About ' . $this->_pageTitle, 'About', $this->_accessLevel, $this->menuHook . '-hire', array( $this, 'about_page' ) );
} else {
add_submenu_page( $this->menuHook, $this->_pageTitle . ' - Overview', $this->_menuTitle, $this->_accessLevel, $this->_hook, array( $this, 'options_page' ) ); // Default
}
}

The variables are defined as follow:

$this->_hook = 'myPlugin';
$this->_file = plugin_basename( __FILE__ );
$this->_pluginDir = str_replace(basename( __FILE__),"",plugin_basename(__FILE__));
$this->_slug = 'my-plugin-demo';
$this->_appIconFile = 'demo.ico';
$this->_selfMainMenu = 'My Plugin Demo';
$this->_menuHook = $this->PARENT_MENU_USERS;
$this->_pageTitle = __( 'My Plugin Demo', $this->_slug );
$this->_menuTitle = __( 'Plugin Demo', $this->_slug );

If I don’t define $this->_selfMainMenu it works and depending on what I put in $this->_menuHook it creates the sub-menu.

I even took part of the code from WooThemes but it doesn’t work so I must be doing something real silly 🙁

Can anyone shad a light on this? Thanks in advance!