Secure Connection Failed – tabs stopped working

Do you have a valid SSL certificate dedicated to your site? Facebook has been working to make SSL mandatory for tabs for a while, but until recently it was still possible to access them via https if you weren’t logged in using an account that had secure connections enabled by default. So you may have thought you had everything configured correctly when you really didn’t. Now, they seem to only be supporting https connections.

I’m not sure if that would explain the error code you reported. Check to make sure you can access the facebook tab manager post on your own website via an https connection.