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GET /error_docs/not_found.html HTTP/1.0" 404 219 "-" "Googlebot/2.1 (+http://www.googlebot.com/bot.html)
Weird, though, because on my logs, the page it requested appears after the 404 entry page URL...the index page of your site didn't have any problems did it?
If your logs are split up into "access" and "error" logs, you can d/l the error log and look at it too and see if you can figure out what it was after.