This comes directly from the help tab on my shopping cart. It might be of some help as to a starting point for you.
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I have enabled SSL but my store isn't loading. What's going on?
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If you have a valid SSL certificate and have enabled secure checkout in your shopping cart, and your site doesn't load in secure mode, it may be because your web server has two separate folders for your store: one for the normal, unsecure HTTP version and one for the secure HTTPS version. If this is the case then when you load your store in secure mode, the HTTPS folder will be empty and you'll see an error such as 404 Not Found.
To fix this and make your store work in both normal HTTP and secure HTTPS modes, you need to ask your hosting provider the following information:
I am trying to setup my application to work in SSL mode, however my web hosting account has 2 separate folders - one for HTTP and one for HTTPS, so can you please create a symlink to redirect HTTPS requests to my HTTP folder? Once you do this my store will work in secure mode.
My SSH details are as follows:
Server: [Type your server here]
User: [Type your SSH user here]
Password: [Type your SSH password here]
Your web hosting provider will then be able to create a symlink for you which will make your store work in both normal and secure modes. You can find your SSH login details in the initial email sent to you by your web host when you signed up, or in your web hosting control panel.