Welcome to WebmasterWorld Guest from 220.127.116.11
I've gone in to GWT, fetched as Googlebot
Having a domain accessible both with and without the www won't confuse a bot any more than texas.example.com and california.example.com would ... Having the same content available on both can create duplicate content issues for algorithms, but it's actually handled by search algo's way better now than it used to be, because they basically just pick one to show in the results when both are available with the same content.
[edited by: TheMadScientist at 6:16 am (utc) on Nov 7, 2012]
I'm seeing it on 2 websites (on different C-class IPs), and one of them doesn't even have a robots.txt file, so the error message can't be correct.