The WooCommerce Subscriptions plugin is currently running its database upgrade routine.
If you received a server error and reloaded the page to find this notice, please refresh the page in -1380635605 seconds and the upgrade routine will recommence without issues. Subscriptions can update approximately 6406 subscriptions before exhausting the memory available on your PHP installation (which has 164M allocated). So depending on the number of subscriptions, you may need to restart the process a number of times.
Rest assured, although the update process may take a little while, it is coded to prevent defects, your site is safe and will be up and running again, faster than ever, shortly.