The issue seems to be linked to your server configuration.
There are a couple of other things you could try to solve the issue.
If you have access to your server configuration settings, please update
PHP_FCGI_CHILDREN from 1 to 2, restart your server, and then try to activate the plugin again.
If you're not sure how to do so, please contact your hosting provider to see if they can help with this.
If that doesn't help, it would be helpful if you could create a php file that contains the following line of code:
<?php phpinfo(); ?>
Then upload it to your site, and send us the link to that file via this contact form:
This will help us sift through your PHP settings and diagnose any issues that may be preventing Jetpack from connecting.