Are you absolutely SURE about that? I've seen many occasions where people thought that was the case and it turns out it was something on their host they didn't even know about, for example.
If that's not the issue, then we have to figure out what else could be causing that. The http:// vs. https:// thing could only potentially come up if you have an SSL installed on your site and you do indeed use https://. So again, if that's not the case it must be something else.
The thing is, if it's neither of those two things I don't have any other general suggestions I can make other than to disable any other plugins you have other than WooCommerce and PayPal for Woo to see if the issue goes away then. You could also try a basic theme like one of the WP included themes just to get everything setup as basic/simple as possible and see if the problem goes away.
If you still can't get passed it we could offer more direct help but I would need you to submit an order for premium support. Then we could get your site credentials and log in there for ourselves to do some testing and troubleshooting.