Nginx error 499

Hi

linode 512

ubuntu 10.04.1 LTS

nginx 0.7.65

php-fpm

xcache (http://xcache.lighttpd.net)

User agents:

__Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html) - normal crawling, etc.

Mediapartners-Google - adsense checks, etc.__

We have lots of 499's on our log…

It seems the mediapartners bot is getting the 499 and then 2 seconds later retries and gets the 200 OK?

What is 499? host unreachable?

Culprit = xcache? but no errors on the xcache control panel, no OOM (out of memory)…

66.249.71.186 - - [11/Jan/2011:13:19:13 +0000] "GET /blog/post155.html HTTP/1.1" 499 0 "-" "Mediapartners-Google"
66.249.71.186 - - [11/Jan/2011:13:19:15 +0000] "GET /blog/post155.html HTTP/1.1" 200 8114 "-" "Mediapartners-Google"

When browsing our own website using Firefox, Chrome, Opera, etc…. I don't experience any errors, normal browsing as expected, website speed is ok…

Thanks in advance for any info.