What's going on here? My NVR and cams will run fine for a couple of days and then out of the blue, one will go black, when I look on the monitor connected to the NVR, I see "log in return time is up". Only way to fix is unplug the ethernet cable and plug it back in. Then it runs fine for a few more days. Happens on 2 different cams, both are HFW4300C cams. I have other HFW4300C cams that don't do this. Any ideas?