After far too long I finally figured out what was rendering the bava to be unreadable on any IP address recorded on the Spamhaus project. Seems like this anti-spam blog plugin for WPMu was the root cause of the issue. What’s odd about this was that the plugin was intended to ban potential spammers from the sign-up page, not the entire site from anyone and everyone who tries to access the site from a suspect IP address. Anyway, the plugin is gone, and hopefully my Spamhaus woes are behind me—sorry for any annoyance that may have cause.