@Varion Am I correct in assuming you followed instructions on this page: https://wiki.fogproject.org/wiki/index.php/Installation_on_Debian_Lenny to install fog?
You might want to (temporarily) disable firewall on FOG server to see if that helps.
A note about other Linux distribution
If you are using other Linux distribution such as Debian / Ubuntu / Suse / Slakcware Linux etc., try the following generic procedure. First, save the current firewall rules, type:
iptables-save > /root/firewall.rules
OR
$ sudo iptables-save > /root/firewall.rules
Next, type the following commands (login as the root) as bash prompt:
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
Mod edited to use code box.