-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.4
This is to let users know of a possible SSL conflict between HikaShop / Joomla and the HTACCESS file. This issue occurs when you have added something similar to the following code to your HTACCESS file:
# force to HTTPS secure site
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule .* https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]
If you have set the Checkout configuration to force SSL on checkout AND you have the HikaShop plugin "HikaShop no SSL outside checkout plugin" enabled, you will get an error page whenever you try to load the website. The issue is that the HTACCESS is trying to force HTTPS whereas the plugin is trying to force non-HTTPS on pages other than the checkout pages.
If you are forcing HTTPS via the HTACCESS file, be sure to disable the HikaShop plugin "HikaShop no SSL outside checkout plugin" and disable the force SSL option on the Checkout configuration.
I hope this helps you as it really took me a bit of time to diagnose, test and find the problem.