Your server successfully processed Google’s request, but isn't returning any content because the connection with the server was reset. Please check back later.
Use Fetch as Google to check if Googlebot can currently crawl your site. If Fetch as Google returns the content of your homepage without problems, you can assume that Google is generally able to access your site properly.
It’s possible that your server is overloaded or misconfigured. If the problem persists, check with your hosting provider.