'Security Header Not Valid" error...

Having trouble with testing new site...when we get to the checkout, have created an account, go to put cc information in, hit next and get the error "Security Header Not Valid" or "Unable to connect to SSL Certificate" or "No shipping method available to that location". Have checked that the SSL certificate is valid and connected properly - our host suggested it is a problem with the cart widget not reading the SSL certificate correctly. Any thoughts? thanks!!
Linda

Could you do screenshots of your browser when you get these error messages ? Except for the "No shipping method available to that location" message, I couldn't find anything about such errors online so we need more details in order to understand what's going on.

The "No shipping method available to that location" message, means that you restricted your shipping methods to zones and other restrictions leading to no shipping methods found for your current cart. If you correct your shipping methods options, it should then not display it anymore.