I have an out of the box Dawn version (upgraded from 9.0.12). It's ran on a plesk. It seems to be working fine. I have some regular readers on a forum. One told me it was 404. I go there it's fine. I deleted MY cookies, Still works fine. Anyways I noticed a huge drop off of good referer traffic. I checked sql sql the hits are listed as invalid. Some show on stats page, some don't.
I got about 6 people telling me the site is 404 and I see it fine. www.keywordcents.com
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You probably have an entry in your antispam blacklist that matches the site they're coming from. in Dawn spammers are shown a 404 page to save you bandwidth. Look through the blacklist for keywords that might match the referring site, and allow them (remove them from the local blacklist).