This is a common DNS problem, I have encountered it myself twice, and I hear about it from others.
I was told it is a common problem with entry-level routers, they hang on a DNS resolve back to their own IP. (I do not know what model of sonic wall equipment you are running, so I'm not implying it is entry-level). For now, I link the site in IE favorites by LAN IP.
Edit: You can always run a nameserver on one of your boxes. I did not want to do that in this case, but it will fix it permanently.