WordPress PermaLinks do not work (mod rewrite enabled + FollowSymLinks enabled + Webserver can write in .htaccess)

I'm facing a serious Problem. The Permalinks in a Wordpress installation I cloned do not work. For example if I have a category "cars" i want the link to look like mysite.com/category/cars. The Original Version was on a different Server than I am working on. I changed the values for "siteurl" and "home" in the Database as well as the Values for 'WP_HOME' and 'WP_SITEURL' in the wp-config.php file. The Database credentials are correct (checked with "ugly" links at first and it worked). Mod rewrite is enabled, the FollowSymLinks option of apache is enabled in the file /etc/apache2/sites-enabled/000-default.conf, document root points to /var/www/mywordpressinstallation and the .htaccess file is writable for wordpress. The apache server version is 2.4.7. The site was previously hosted on an NGinx server could that be something which collides with our server?

/etc/apache2/sites-enabled/000-default.conf file:

<VirtualHost *:80>

    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/mywordpressinstallation
    <Directory />
            Options Indexes FollowSymLinks MultiViews
            AllowOverride All
            Order allow,deny
            allow from all
    </Directory>
</VirtualHost>

.htaccess file:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

The site i am working on also has a custom build plugin for it. I am not shure if this could also be the cause of the problems since it is not a standard build WP Plugin.

Thanks in Advance for the answers

Solution

I solved the problem unexpectedly. I just copied a default.conf from a server that already works and just edited the document root path. After examining it turns out I gave apache the wrong path to my folder. You have to write out the whole path instead of your relative from the DocumentRoot ex. "/" would be wrong but "/var/www" would be correct if you want to set rules for that path, eventhough you already set the DocumentRoot path to "/var/www" you still have to write the whole path.