What are the camera models? Are they the same model? Is the second cam bricked? If the second cam that is giving you a issue after the upgrade and is working, you can usually backup the config file from the working camera and upload it to the second camera. If the camera is bricked, you might be able to go in through the back door. Doing it through the back door is not in my skill set but depending on the cam model, a lot of people have done just that.