public function postAdminAddGroup($id = null)
    {
        // Get user information
        $user = Sentinel::findById($id);

        if ($user == null)
        {
            // Prepare the error message
            $error = Lang::get('base.auth.not_found');
            return View('layouts.modal_confirmation', compact('title', 'message', 'error', 'model', 'confirm_route'));
        }

        $gid = Input::get('group');

        if ($gid == null)
        {
            // Prepare the error message
            $error = Lang::get('base.groups.not_found');
            return View('layouts.modal_confirmation', compact('title', 'message', 'error', 'model', 'confirm_route'));
        }

        // Get group information
        $group = Sentinel::findRoleById($gid);

        if ($group == null)
        {
            // Prepare the error message
            $error = Lang::get('base.groups.not_found');
            return View('layouts.modal_confirmation', compact('title', 'message', 'error', 'model', 'confirm_route'));
        }

        // Remove the group
        $group->users()->attach($user);

        // Prepare the success message
        $success = Lang::get('base.groups.added');

        // Redirect to the user management page
        return Redirect::route('users.update', $user->id)->with('success', $success);
    }