Install Haproxy On Bsd Ports
Apache Haproxy
Haproxy Port Forwarding
Probably you can try to lower down the value of maxconn in haproxy.conf? I'm running too, and I don't have such issue. I installed it from port, and I suggest that you use the haproxy from the ports tree as well, since it is the proper way to install it on FreeBSD, plus it will make it easier for you to update it in future.And like SirDice mentioned in previous post, it is better for you to put your configuration file in /usr/local/etc, since configuration files for ports/packages reside there, and not in /etc. If you install it from port, that's where the configuration file will be placed.