It was only the website, mining was proceeding as normal. The web server process locked up and did not respond at all.
BitFORCE (/dev/cu.usbserial-00001324) ERROR: Extraneous data received: NONCE-FOUND:737AD686
2012.09.08 [22:02] BitFORCE (/dev/cu.usbserial-00001324) ERROR: ZFX command timed out. Retries: 0
If the BFL unit takes too long to respond you get a timeout message. If later it finally sends a response you get an "extraneous data" message because the miner is no longer expecting any response.
If you get a lot of that it can be because your BFL units are throttling. When they throttle they stop responding for a moment.