After adding a product to the cart, I see it on the cart page, I see it in the left column cart, and I see it the View Cart link at the top drop down. However if I choose the Checkout button from either the left column Cart or the top dropdown cart window, it says there are currently no items in the cart and the item disappears from everywhere.

If I hit the browser back button , it shows up again in all 3 places. But the only way I can actually get to checkout is if I use the checkout button at the bottom of the main window.

Also some pages including the shopping cart page says not secure. But the other pages in the site have the security lock including the home page.

Most often this is a situation where your site is flipping between www and non www url's and the same possbily with https and non-https
This should be forced in your htaccess file and there is info here on that.
It should also match the form of the URL in your admin main settings.
https://www.ecommercetemplates.com/support/topic.asp?TOPIC_ID=114720
David

This seems to have fixed the issue.

Should I also add:

"If you want to force users onto a secure https connection when they visit the first cart screen of checkout add the following to includes.php

$cartpageonhttps=TRUE;

quote:

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Should I also add:

"If you want to force users onto a secure https connection when they visit the first cart screen of checkout add the following to includes.php

$cartpageonhttps=TRUE;

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This is not needed when you force the entire site on to https, which for a few years now, is the standard practice for all websites these days.
If your site is not on full time https, google will demote your site.
All e-commerce websites should be on full time https.

David