Couple of days back Google sent out a message to many site owners, that there is a problem with their site.
Google told these webmasters that "Googlebot can't access your site", that the site had connection failures and Google was unable to access your site.
Here is Google's Matt Cutts wrote in the thread that this seems like an error on Google's side. He said:
"Hey everyone, please don't worry about this message at this point. Enough people are getting this message that I suspect it's an issue on our end.
I've got an email out to our webmaster tools team, and we'll figure out what's going on. Thanks."