On Call of Duty Black Ops?

I have been playing Black Ops since it came out on my sisters PS3 now I got mine I've got mine wireless and hers wired to the router that we both use but when I try to make a party with her in the room it kicks me out or her out of the room when we launch or sometimes it tells me her session is no longer active and I can see her screen she has everyone she plays with waiting for me to get in I've even jumped in while in game lobby and does the same and Oh I have static IP on my PS3 which I dmz. Any help I have a netgear cable modem/wifi router