Laravel Login with Sentry

Question

I am new to laravel and am trying to implement a login feature with sentry where by i have two groups in the database,the 'admin' group and the 'user' where by each group will be redirected to their respected views,but this gives me the following error

Symfony \ Component \ Debug \ Exception \ FatalErrorException (E_ERROR) Call to a member function inGroup() on a non-object

Open: C:\wamp\www\library\app\controllers\UserController.php

The area points to this area of the code

  {
        echo 'User is suspended.';
    }
    catch (Cartalyst\Sentry\Throttling\UserBannedException $e)
    {
        echo 'User is banned.';
    }
    $user = Sentry::getUser();
    $admin = Sentry::findGroupByName('admin');
    $users = Sentry::findGroupByName('user');

    if ($user->inGroup($admin)) return Redirect::intended('admin');
    elseif ($user->inGroup($users)) return Redirect::intended('user');

Here is my complete code for the login process

    public function postLogin(){
    try
    {
        // Login credentials
        $credentials = array(
            'email'    => Input::get('email'),
            'password' => Input::get('password'),
        );

        // Authenticate the user
        Sentry::authenticate($credentials, false);
    }
    catch (Cartalyst\Sentry\Users\LoginRequiredException $e)
    {
        echo 'Login field is required.';
    }
    catch (Cartalyst\Sentry\Users\PasswordRequiredException $e)
    {
        echo 'Password field is required.';
    }
    catch (Cartalyst\Sentry\Users\WrongPasswordException $e)
    {
        echo 'Wrong password, try again.';
    }
    catch (Cartalyst\Sentry\Users\UserNotFoundException $e)
    {
        echo 'User was not found.';
    }
    catch (Cartalyst\Sentry\Users\UserNotActivatedException $e)
    {
        echo 'User is not activated.';
    }

    catch (Cartalyst\Sentry\Throttling\UserSuspendedException $e)
    {
        echo 'User is suspended.';
    }
    catch (Cartalyst\Sentry\Throttling\UserBannedException $e)
    {
        echo 'User is banned.';
    }
    $user = Sentry::getUser();
    $admin = Sentry::findGroupByName('admin');
    $users = Sentry::findGroupByName('user');

    if ($user->inGroup($admin)) return Redirect::intended('admin');
    elseif ($user->inGroup($users)) return Redirect::intended('user');

}