The error in the log is fine; it just means it didn't find "mail.marlborosurvey.net" in the Domain list. Then it tested Subdomains and got a match, which is why the second line went away and the mail is now signed.
The signature failure is probably caused by you using sendmail's "MASQUERADE" feature. Your signing filter sees "mail.marlborosurvey.net", but I can tell from the reply that what sendmail.net sees is just "marlborosurvey.net". So what gets signed and what gets received aren't the same, so the signature will fail.
You need to turn off masquerading, or generate mail with a From: that's in the main domain, not in the "mail" subdomain.
From: Jason Clint [mailto:nosaj_17_at_hotmail.com]
Sent: Tuesday, October 26, 2010 2:20 PM
To: Murray S. Kucherawy; opendkim-users_at_lists.opendkim.org
Subject: RE: Signing problem
By the way in case you where wondering what I did to the opendkim.conf file I just set "subdomains yes".
________________________________
From: nosaj_17_at_hotmail.com
To: msk_at_cloudmark.com; opendkim-users_at_lists.opendkim.org
Subject: RE: Signing problem
Date: Tue, 26 Oct 2010 21:12:37 +0000
Ok so now I am getting a different error:
Received on Tue Oct 26 2010 - 21:23:26 PST
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