SSL Insecure content

OK,

I have made changes in ~common\header.php in both catalog and admin.

No difference, so it's not that simple.

Any other files that you found?

I can confirm as with others, that if I make http and https settings in config, all to "https" - then error disappears.

RobinD

This issue can occur when you enable your site to work under https and when your hosting provider uses an SSL Reversed Proxy / Load Balanced SSL Proxy. You can check to see if your host is using SSL load balancing / proxy, and if so there is now a vQmod available to fix any issues that you are experiencing with OpenCart:
http://www.opencart.com/index.php?route ... n_id=11280