Paths not working?

[kobra]

Did you attempt to manually edit/enter these or allow the installer to do so??

  define('HTTP_SERVER', 'https://www.site.com');
  define('HTTPS_SERVER', 'https:/www.site.com');

Missing a "/" there

// * DIR_FS_* = Filesystem directories (local/physical)
  //the following path is a COMPLETE path to your Zen Cart files. eg: /var/www/vhost/accountname/public_html/store/
  define('DIR_FS_CATALOG', '/var/www/vhosts/site.com/httpdocs/shop/');

Are you sure that this is your correct path???
var, www, and vhosts are normally replaced with your actual variables for them

define('DB_SERVER', '127.0.0.1');

127.0.0.1 is usually "localhost" but is this is working leave it alone

[quixotic]

unbelievable... I must've looked at that file a few dozen times, and for some reason never saw the missing backslash. so sorry to waste your time, but yeah, that was it. Thank you so much for pointing it out, I really appreciate it.

For what it's worth the latter half, the /var/www/vhosts/... is correct. It's PLESK's default directory structure (at least in CentOS), and it's where it places all of it's virtual hosts.

[kobra]

I would suggest that you change this as Zen Cart is smart enough to auto switch for only those pages that require https

  define('HTTP_SERVER', 'http://www.site.com');
  define('HTTPS_SERVER', 'https://www.site.com');