I have read several complaints in this forum lately about port forwarding not working properly, and just to clarify, port forwarding is from WAN to LAN which still works fine, most users are having problems with loopback (LAN to WAN to LAN or LAN to LAN). The way dd-wrt implements it currently will not work for most setups, to fix it, you can go to the webgui in dd-wrt under Administration > Commands and enter in this code, once the code is entered, click "Save Firewall" and restart the router. 

iptables -t nat -I POSTROUTING -o br0 -s 192.168.1.0/24 -d 192.168.1.0/24 -j MASQUERADE

Of course if you use a different subnet than 192.168.1.1 you'll have to adjust the code to work for what subnet you use. Also, another great code, which i hope will soon be implemented into dd-wrt is.. 

insmod ipt_mark
insmod xt_mark
iptables -t mangle -A PREROUTING -i ! `get_wanface` -d `nvram get wan_ipaddr` -j MARK --set-mark 0xd001
iptables -t nat -A POSTROUTING -m mark --mark 0xd001 -j MASQUERADE

Which can also be saved in Administration > Commands enter the code then click "save firewall"

This code adds loopback for ALL interfaces regardless of how many different subnets you use.