Port Forwarding on a nonexistent device

[aChipmunk]

After my modom was rebooted, I went to change my port forwarding rules because my ip changed.  Now when I try to apply, deactivate, or delete one of my rules, it says it is being used by an ip that does not exist on my network.  If i try to make a new rule with the same ports i get and error when i apply it.  How can i delete or deactivate the rule that is in use?

[dslr595148]

What is the brand and model of this modem combo?

[aChipmunk]

I have a gt704wgb modem + router.

[dslr595148]

Ok, there is more than one guide.

#1 Go to http://portforward.com/

#2 Please tell me which guide best shows the screens of your router.

Thanks,