I am having the same issue, and it just started after upgrading to WP 2.6. I did a search for 'class snoopy' in the forums, and found this and several other posts. I'm seeing this issue not only on the dashboard (specifically with 'Incoming Links'), but also when I try to activate certain plugins (wordpress.com Stats Helper).
When I just recently tried to post an article, I hit the publish button and then saw the error on a separate page. The article posted fine, but I got the error page instead of a blank post like it did before.
If I knew more about the functions of the snoopy.php file, I might be able to troubleshoot it on my own, but I have no idea how it's used or why I might be seeing this error. Any help would be appreciated - thanks.