Your posting dates from October. Have you been able to resolve the problem?
I have just started experiencing a similar problem after installing the (Pirelli) Centro Grande router (supplied by Swisscom). IP forwarding works OK for a PC web application, but not for an IP camera. Needless to say, I had no such problems with my previous router (Motorola Netopia also supplied by Swisscom). Since the router is the only component that has changed in my configuration...
Thanks,
-- Bob