Invalid link: Cannot load presenter ‘Post’, class ‘App\Presenters\PostPresenter’ was not found

I am new to Nette Framework I really like it but I am facing a problem even everything is ok according to the tutorials but it shows me the following warning, Please answer in English, I saw some solutions while searching but that was all in other language so it was not useful for me. I asked the same question on stackoverflow but there are very limited question about Nette there and I think Nette is not widely used outside Check Republic even it a very nice framework.
Invalid link: Cannot load presenter ‘Post’, class ‘App\Presenters\PostPresenter’ was not found.

<?php

namespace App\Presenters;

use Nette,
    Nette\Application\UI\Form;


/**
 * Post presenter.
 */

class PostPresenter extends BasePresenter
{
    /** @var Nette\Database\Context */
    private $database;

    public function __construct(Nette\Database\Context $database)
    {
        $this->database = $database;
    }

    public function renderShow($postId)
    {
        $this->template->post = $this->database->table('posts')
        ->get($postId);
    }
}