Jetpack works wonders on two of my sites, but on a third, http://www.montrosehamradio.org, even placing it in the plugin directory causes the site to crump and deliver only blank pages.
Could you try to download a fresh version of the plugin from the plugin page, and then install the plugin to your site by following these instructions?
if that doesn't help, you will need to access your server error logs, in order to know more about the errors that trigger the blank pages on your site.
Once you have found the error, could you post it here so we can have a look?
If you don't know how to access your server error logs, your hosting provider should be able to help.
Hi, I just tried again. I installed Jetpack by finding it on the Plugins admin page and clicking on install. It claimed to install correctly, but then the site hung. I used Plesk to delete the Jetpack directory in the Plugins directory, and the site immediately began functioning again. This generated only a single line in the error log: "[Thu Feb 28 06:10:06 2013] [warn] (70007)The timeout specified has expired: mod_fcgid: can't get data from http client" I have no idea what this means!
It sounds like the server is timing out in it's connection to WordPress.com, maybe. Are your other 2 sites on the same server? Also, can you please try installing the Jetpack Compatibility Plugin so we can see some additional information from your site?
1) Download the plugin from http://plugins.svn.wordpress.org/jetpack/branches/jetpack-compatibility-test.zip
2) Upload the plugin to your site via Dashboard -> Plugins -> Add New.
3) Activate the plugin and go to Plugins -> Jetpack Compatibility Test.
4) Click the "Select All" button.
5) Send the results in an email to firstname.lastname@example.org (do not post it here)
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