Wordpress problem

http://imageupload.com/out.php/i806_WTF.PNG

can anyone help me, why I get this error?
Thanks

Forbidden You don't have permission to access /wp-admin/admin-ajax.php on this server. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. Apache/1.3.37 Server at www.rockscene.net Port 80

get this error when I delete Post or if I want to add a category

http://imageupload.com/out.php/t828_WTF2.PNG

this is error when I try to delete post...

so there is something wrong with:
- admin-ajax.php
- index-extra.php

You might be missing file be sure to check and if needed to re-upload them.

I reuploaded all files.. still not working

Are you installing WordPress manually or you use Fantastico or any other autoinstall ? If you use an autoinstall script provided by your hosting provider i would consider contacting them. Otherways, if you manually upload the files on the server check that you are doing it in the proper way, and if you are sure you are doing it the proper way, the only suggestion i can give you is to contact your web hosting company and ask them to look into it.

I have no problems with WP on my server.