I have a subdomain and Google Webmaster Tools, told me this:
Googlebot can't access your site
This is not the first time that I receive this message from Google's Webmaster Tools.
I need to should I contact my hosting company technical support? In other words, is it a problem related with the server?!
Also I noticed a great decrease of traffic to my website after receiving this message from the first time. I have set many subdomains on my web host, and some of them is not exist, i.e. its directory is deleted.
The following is a copy of the message from Google's Webmaster Tools: