The exception number is a timestamp that gives you a hint when the error occured and had been logged in the server log. In human readable form the time/date is Sunday 7th October 2012 @ 22:25:10pm GMT. Check out your server log for entries around that time for more information about what's wrong.
Is this a new site, or did you transfer it from somewhere else? I usually see that when I copy the codebase, including the settings.php but don't have a valid database yet.
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