Problem Playing Natural Selection

Apocalipsus

<div class="IPBDescription">And using zone alarm firewall</div> 2 of my friends who play the game and use this firewall (zone alarm) don't have any problem playing, but me when i play ina server and i have the firewall on i have pings around 600 or even more , i then shutdown the firewall and my ping goes back to its normal (30-50), i try then to turn on the firewall again but the same thing happens, pings boost up to 600.
The problem is that this is the only game where this happens and i dont know what to do.

FireStorm

I've used this firewall too and I didn't have any problems.

Try to set full permissions to hl.exe, or try to upgrade the firewall if you don't have the latest version.