Don't know the age of the camera but my guess is that it is older and is looking to use admin as the password. I would either remove the camera from your POE NVR and connect to POE switch or connect using 12v and ethernet to your router/hub/switch. and log in using admin admin.. Or just change the password in the cameras device config area to match admin admin and just make sure to change it because you don't want to leave default like that.. Anyway if you did put in switch on your network using IP config you can modify password there by logging in to it. Then it will prompt you to change the password. Make same as you use on your NVRs cameras.. THen you can install back to the NVR.. My guess is that installing the other cameras didn't increase the other cameras wattage it was caused by the cameras watt needs either change in light conditions and or other factors depending on the cameras options.. Anyway my guess is that the camera needs you to setup with old admin admin if you can't either Initialize it with that function in the NVR or if you don't want to just add it using admin as the password until you change the password after a connection to the cameras WebUI at some point in the future.. Just make sure if you do add it by changing the password in the NVRs device area clicking on the pencil and changing the password there. YOu will want to make sure you change the password soon after so it don't got changed later and forget to make the update yet again in the cameras setup area on the NVR. Not all OEMs act like Dahua cameras on a Dahua or other OEM NVRs..
Yeah easy test in that page that bigredfish just said you should go to. CLick the pencil and put admin for password if it changes to Green that was the issue. Then click the e to log into the camera and it will prompt you to change the password then change password and save, exit the cameras WebUI, then back at that page again click pencil again and update the password to what you just setup and it should remain on your NVR from there on..