Dead Space 3 Coop disconnects after 20-30 minutes play

Hello, Me and my friend started playing DS3 Coop and are enjoying it. But there is a litte problem: When we connect the 1st time, we have no problem connecting and starting the coop but after ~20 minutes of normal playtime the "connection interrupted" error shows up and then the game disconnects. We(me and my friend) are using skype the whole time to communicate and we can talk with no problems. Help please.