Major problem with live site (login/checkout/create_account loop)

[ckyshop.co.uk]

Have a major problem with my site, RockShopDirect.co.uk in that on some, but not all, computers it is impossible to purchase goods.

 

When a customer adds an item to the cart and then clicks checkout after they create an account the cart has been emptied. The same thing happens in various circumstances; I think it's something to do with either passing between http and https, cookies or sessions. And in mentioning those three, on a separate note, I also have major problems with my whos_online.php.

 

I think this might be similar to [This topic] but there is no real solution mentioned there.

 

Thank you very much for your time.

[ckyshop.co.uk]

Here is configure.php

 

  define('HTTP_SERVER', 'http://www.rockshopdirect.co.uk'); // eg, http://localhost - should not be empty for productive servers
 define('HTTPS_SERVER', 'https://www.rockshopdirect.co.uk'); // eg, https://localhost - should not be empty for productive servers
 define('ENABLE_SSL', true); // secure webserver for checkout procedure?
 define('HTTP_COOKIE_DOMAIN', 'rockshopdirect.co.uk');
 define('HTTPS_COOKIE_DOMAIN', 'rockshopdirect.co.uk');
 define('HTTP_COOKIE_PATH', '/');
 define('HTTPS_COOKIE_PATH', '/');
 define('DIR_WS_HTTP_CATALOG', '/');
 define('DIR_WS_HTTPS_CATALOG', '/');
 define('DIR_WS_IMAGES', 'images/');
 define('DIR_WS_ICONS', DIR_WS_IMAGES . 'icons/');
 define('DIR_WS_INCLUDES', 'includes/');
 define('DIR_WS_BOXES', DIR_WS_INCLUDES . 'boxes/');
 define('DIR_WS_FUNCTIONS', DIR_WS_INCLUDES . 'functions/');
 define('DIR_WS_CLASSES', DIR_WS_INCLUDES . 'classes/');
 define('DIR_WS_MODULES', DIR_WS_INCLUDES . 'modules/');
 define('DIR_WS_LANGUAGES', DIR_WS_INCLUDES . 'languages/');
 define('DIR_WS_CACHE', DIR_WS_IMAGES . 'imagecache/');

[ckyshop.co.uk]

Seem to have solved this by disabling "Check IP Address" in Admin > Sessions.