As
said implied by bigredfish, 'unable to find network host' means the NVR cannot find the camera and connect to it.
Compared to bigredfish's photo.... you have NVR GUI 4.0 version (red bell for TiOC function). So your camera status web UI will look like this:
In the corner of your camera, you will notice a little RJ45 port symbol.
This means the NVR recognises this channel is a camera connected directly to the NVR's built-in POE switch.
No RJ45 symbol means the camera is powered off and/or not responding to data.
My guess is your installer setup each camera manually rather than letting the NVR handle DHCP leasing and automatic plug & play.
So the NVR thinks each camera has a static IP address (the numbers shown on each channel) but it cannot find a camera on that address.
Try searching for devices and see if the NVR finds them all.
If your NVR does find all the cameras; delete all the un-connected entries first, then select all the found cameras and add them back.