Jetpack installation problem

I accidentally deactivated Jetpack a few days ago. It had been running happily on my site (http://www.jpehs.co.uk) for about a year. When I clicked to reactivate it I was asked, as I had been initially, to connect to WordPress.com to activate it fully. But attempting to do this threw up an error message that is very familiar from a number of other forum discussions:

Your website needs to be publicly accessible to use Jetpack: site_inaccessible Error Details: The Jetpack server was unable to communicate with your site [HTTP 0]. If you are hosted with Go Daddy, they are aware of this issue, and we at WordPress.com are working with them to fix it. If your site is hosted elsewhere, please contact Jetpack Support: http://jetpack.me/support/

I’m running the latest version of WordPress and have the latest version of Jetpack. None of the solutions I’ve found on other forums help. I asked my host to relax the permissions on the entire site to ensure that xmlrpc.php was writeable (that’s something that was suggested as a likely cause) and I’m not using Go Daddy or running the W3 Total Cache (two other likely suggested problems). I’ve written to the Jetpack support team as requested in the error message but received no reply.

If anyone has any idea what could be going wrong here — maybe it’s just a glitch with the current version of Jetpack, which will be sorted out soon — I’d be really grateful. I’d really like back the functionality of this plugin.