Do you have your store url set to (https://www.yours.com/) ?
Have SSL enabled as well.
And do not have force ssl set on the web server configuration (not a nop setting).
In IIS there is a setting to force ssl on the configured website your running your site on, I found when you have this set to on it will cause the error you stated. The nopCommerce configuration will enforce your store to use ssl.
Check with your web hosting provider if you do not have access to the webserver configuration.