I know this is not WPMU related but I thought I'd share anyway. I noticed via Google Webmaster Tools that I had a sitemap error. After checking and re-submitting the sitemap the submission came back with the same error. I decided to do a Googlebot check and this also returned an error.
I contacted my host, I'm on a shared hosting account, and reported the issue. Their response was as follows:
Thank you for contacting TMDHosting Technical Support Team!
Due to the fact that the Google bot sometimes crawl at very aggressive speed it cause some severe overload on the server. This combined with the fact that Google very often changes their network ranges for it, our firewall mistakenly has blocked it. I have now flushed the firewall and Google bot should not experience problems crawling your website.
Please, do not hesitate to contact us again if we could be of any further assistance! We are 24/7 on your immediate disposal!
Lol, Very aggressive speed. Has anybody else experienced anything like this before? I find it really weird.