When error happens, NSB-25 shows error code on LCD.
Please inform us the error code to figure out the reason of the error.
Also, if your firmware version is not latest one, please try upgrade firmware at here.
https://www.nextodi.com/support/download-view/?id=201

Please note.
We changed the folder structure from V1.30.
If your disk(either internal or external) contains backup folders from both format folder, then it will make error.
In that case, move old format backup folder to other place outside [NSBROOT] folder and try again.