At first when I put the index.php and the flatboard.zip file in my directory and go to the url it sais:

Notice: Use of undefined constant PATH_ROOT - assumed 'PATH_ROOT' in D:\LP_Werk\_dev\flatfileforum\www\1.0\public_html\index.php on line 34

When I ignore this and go through with the installation i get a second error: Notice: Constant JSON_PRETTY_PRINT already defined in D:\LP_Werk\_dev\flatfileforum\www\1.0\public_html\init.php on line 44

When I ignore this and add a new forum I get redirected to a 403 forbidden page that sais: You don't have permission to access /index.phporum on this server.

Does anyone know what the problem is I run flatboard on localhost.

Hey anonymous user,
This bug will be fixed in the next version.
This bug is only present when you run Flatboard on Windows.
While waiting for the update, here is how you can fix it:

Replaces the lines :
1. init.php, line 44 :

if(!defined('JSON_PRETTY_PRINT')) define('JSON_PRETTY_PRINT', 128);

2. add.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

3. auth.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

4. blog.php, line 12 :

require_once __DIR__  . '/' .  'header.php';

5. config.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

6. delete.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

7. edit.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

8. feed.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

9. header.php, line 16 :

const DS = '/';

10. index.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

11. install.php, line 12 :

const DS = '/';

12. lib/Captcha.lib.php, line 15 :

	 'font_path' => __DIR__ . '/' . 'arial.ttf',

13. plugin/identicon/autoload.php, line 20 :

        $fileName = str_replace('\\', '/', $namespace) . '/';

14. plugin/identicon/autoload.php, line 22 :

    $fileName = __DIR__ . '/' . $fileName . $className . '.php';

15. search.php, line 11 :

require_once __DIR__  . '/' .  'header.php';

16. view.php, line 11 :

require_once __DIR__ . '/' . 'header.php';

  Yes a update with all these corrections come soon 👌

The last release correct this error, i close this thread.
If you have other errors, thank to open new thread.