Bizarre Mac Wi-Fi Problem

I’m the first one to admit that Apple devices aren’t perfect. On balance, however, I find that they fit my needs better than competing products. Your mileage may vary.

But, usually, They Just Work™.

However, I’ve encountered a bizarre problem with one of my MacBook Pros. (Oddly enough, with the office unit, which I keep pretty pristine. I run all the weird experimental stuff on the unit at home.)

Safari doesn’t work on Wi-Fi.

Firefox and Chrome work fine. But Safari just displays blank pages with “You aren’t connected to the Internet.”

I thought it might be a weird setting on GT’s routers, so I brought it home tonight. Plain-vanilla Belkin router with WEP security. Same problem. The Network settings in System Preferences are identical to my home Mac, which works fine.

And Safari runs fine with the Ethernet cable connected, so it’s only with Wi-Fi.

I deleted and reinstalled the latest version of Safari from Apple’s Web site. Then, in frustration, I handed it off to my tech support staff, who reinstalled Snow Leopard and all the latest updates.

Safari doesn’t work on Wi-Fi.

Neither do most other network applications, but not all: Evernote and Tweetie both fail. Mail.app fails, but Thunderbird works fine. System Update fails, but Network Diagnostics shows six green balls and “Your connection appears to be working.”

This laptop has certainly worked with Wi-Fi in the past — I travel with it — but I don’t remember the last time it worked, or anything I’ve done that could make it fail.

I have absolutely no idea what to do. I stay pretty up to date on this stuff, and it’s stumped me, plus two employees who I pay to stay up on this this stuff. Any suggestions?