Ok, so that problem is resolved, but now it looks like you may be having an open_basedir problem:
Fatal error: main(): Failed opening required 'includes/application_top.php' (include_path='.:/usr/share/pear') in /home/httpd/vhosts/yourdomain.com/httpdocs/shop/index.php on line 13
or maybe a path error in a config file for the application.
include_path='.:/usr/share/pear'
My eyes are not so good, but is that a period and colon before the /usr/...
Check your /home/httpd/vhosts/yourdomain.com/conf/vhosts.conf file. If you (hopefully) have a statement for php_admin_flag open_basedir ... statement, check it for typos.
This is what I would normally put in for an osCommerce type site:
<Directory /home/httpd/vhosts/yourdomain.com/httpdocs>
php_admin_flag engine on
php_admin_value register_globals 1
php_admin_value safe_mode 0
php_admin_value open_basedir /home/httpd/vhosts/yourdomain.com/httpdocs:/tmp:/usr/share/pear
</Directory>
1=on, 0=off (had to do this with current PHP on RH), if the numbers don't work, then use on and off. Also if you are doing an SSL site, then change the 'httpdocs' to 'httpsdocs' in the lines above.