I'm unsure why the Social Debug Tool is reporting that error. It seems like the SSL certificate isn't being read properly from your site, but I don't think it's an issue with your site and instead a problem with Social Debug.
I'd recommend using Facebook's own Debug Tool instead. It can provide similar information as to what Open Graph tags are set on the page and how a share would look:
developers.facebook.com/tools/debug
Sorry for the inconvenience. I hope that helps,
Alex