Webuser Forums: what could be stopping google

Over a month now I still cannot find a solution.
My server is never down and I rarely have error pages, its been the same for 6 years, a very busy site.
Nothing has really changed.
could you tell me what could be stopping google, I have not been
banned for anything, else it would not come on my site at all..
Googlebot last successfully accessed your home page on Oct 15, 2007.

This page lists URLs from your site that Googlebot had trouble crawling.
Network unreachable [?] Sep 16, 2007
503 (Service unavailable)Sep 9, 2007
503 (Service unavailable) [?] Sep 12, 2007

There are many more
I have no traffic shown in my statistics for google at all for this site

Why would the network be unreachable or unavailable on all my pages?
I found that google is comming up with Network unreachable and service
unavailable for this site, but I have had no down time or error pages.
I feel something is blocking this site.

I did have this happen once before when I became busy with a host in England, they stopped any traffic to my site, because I have a very busy site and used too much bandwidth.

But I pay for 80gb a month. and they say everythings is working o.k

Please help