As ppl have said above ::
1. Visit portforward.com
2. Find our router name and model no. (check on bottom of router)
3. Find the correct router or the nearest similar eg. If u have Motorola 7710 and they say 7700, try that .. it may be almost SIMILAR .. The correct option just may be under another suboption .. eg. Its like finding Save option under EDIT instead of File -> Save
4. If it still shows error, set port no. 54848 (around this value as it is an open port..) and SWITCH OFF PORT RANDOMIZE.
5. Then add this port to ur Antivirus (Important :: Kaspersky i had to open it .. or i simply disabled proactive defense in Kaspersky ..)
6. Do the same in firewall.
It should wrk now, otherwise ur doing something wrong. I have configure 4-5 frnds comps following this list from 1-6 and it always works. hope it helps.
ciao.