A few months ago I started noticing that Gametracker sometimes reports my BF2 server as 'Down' when it's actually up. The problem usually seems to resolve itself after a few hours, but it happens several times per week. While this is happening, the server appears in the in-game server browser, and I can join the server and play without any trouble. If I click the 'Dead' link on the server's Gametracker page, then click 'Update scanning parameters', sometimes that fixes the problem, but often it says 'Could not scan server'. Any idea what's going on?

Sounds like some of these IPs are being blocked by your firewall. I would suggest checking that and possibly whitelisting the IPs.

http://www.gametracker.com/forums/forum.php?site=1&thread=108247