The error is a resource protection mechanism, not a bug. It tells you that your NVR has hit its simultaneous decoding limit. By understanding your device’s specifications, managing online users, and adjusting client software settings (like iVMS-4200's playback channel limit), you can quickly resolve the issue and regain access to your footage.
Are you seeing this error on the mobile app or on the NVR's local monitor ? The error is a resource protection mechanism, not a bug
for playback if available, or lower the camera bitrate in the device's encoding settings. Outdated Firmware managing online users