Two Google Webmaster Help threads have complaints from webmasters and SEOs that the fetch as Googlebot feature in Webmaster Tools is not working.
Specifically, people are running it and are being returned a 404 error that reads:
Webmaster Tools - 404Oops!
The page you are trying to reach does not exist (404).
Google's JohnMu chimed in over the weekend to say he will send it up the chain to be fixed. He said:
Thanks for your report. I'll pass it on to the team to review and get back to this thread once I know more.
I personally tried it a couple times and it worked for me but it might be a sporadic issue.
Forum discussion at Google Webmaster Help.

Comments:
ragz
11/01/2010 12:58 pm
Definitely something happening with my sites and webmaster tools.In webmaster tools i am getting messages that my site is is not accessible.Normally it indexes every day and indexes about 100-150 new pages everyday.But it is not updated from 2 weeks.