Hi,
Sounds like you're doing searches and this leads me to believe that it's something HTTPS related. When you're doing HTTPS filtering and have a Content Modification policy for Google Force Safe Search, the latter takes precedence. I've had a few customers who were using Safe Search and seeing questionable results. As soon as we've disabled the content modification, there was enough content for the Smoothwall webfilter to be triggered, thus blocking those results.
If this isn't the case though, can you be a bit more specific about your setup? Are you doing HTTPS DnI? What's the website or search term in question?
Dan