DOS 42 Connections. During a DOS attack, the server's firewall becomes extremely sensitive to high connection counts (it's worth nothing that this is not normal behavior and is only temporary, it's just a mitigation we apply when a botnet hits us to avoid our servers going down). You said you're working with MySQL...are you using remote MySQL? If so, that can cause this as well. Also, if you're constantly refreshing your website (especially one with lots of graphics/CSS/scripts) as part of testing/development, that can also trigger this. Once the attack ends and the mitigation is lifted, this won't happen anymore. Unblocked again.