I got this message on Hostgator when I set up a testing server. The problem was that WordPress could not connect back because of an ssl certificate mismatch (I was using shared hosting).
I changed:
https://123.456.789.0/~myuser/mySite.com/
to
https://123.456.789.0/~myuser/mySite.com/
in the wp_options table for “site_url” and ‘home’ values so that there was no ssl certificate involved and it fixed the problem and Jetpack was able to connect.
