What does error 158 mean when running a backup?

Hello.

Implementing a backup routine, I ran a full backup on one of my directory ring servers in a development environment. I used the command:

dsbk backup -b -f /path/FULL-DSBK-HOSTNAME-TREE-NAME-DATE_TIME.bkup -l /path/FULL-DSBK-HOSTNAME-TREE-DATE_TIME.log -e XXXX -t -w -a

The backup succeeded but ndsd.log sent me the following output with error 158:

Command line   backup -b -f /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREE-NAME-DATE_TIME.bkup -l /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREE-NAME-DATE_TIME.log -e XXXXXXXXXXXXXXX -t -w -a
Processing command line
Backup type: Full
Log file name: /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREENAME-DATE_TIME.log
Backup started: 2021-12-15'T11:50:49
Backup file name: /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREENAME-DATE_TIME.bkup
Server name: \T=TREENAME\O=system\OU=servers\CN=HOSTNAME
Current Roll Forward Log: 00000039.log
DS Version: 4010509
Backup ID: 61BA2AF9
NICI BACKUP: "NICI Files have been backed up Successfully"
Starting database backup...
Error!: -158
Database backup finished
Completion time 00:00:00
1 Error!
DSBK error! -158

And FULL-DSBK-HOSTNAME-TREE-NAME-DATE_TIME.log shows me the following output:

|==================DSBackup Log: Backup================|
Backup type: Full
Log file name: /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREENAME-DATE_TIME.log
Backup started: 2021-12-15'T11:50:49
Backup file name: /opt/backups/dsbk_store/HOSTNAME/fullbk/FULL-DSBK-HOSTNAME-TREENAME-DATE_TIME.bkup
Server name: \T=TREE-NAME\O=system\OU=servers\CN=HOSTNAME
Current Roll Forward Log: 00000039.log
DS Version: 4010509
Backup ID: 61BA2AF9
NICI BACKUP: "NICI Files have been backed up Successfully"
Starting database backup...
Error!: -158
Database backup finished
Completion time 00:00:00
1 Error!

I can't find references to this error, could you help me with the meaning and consequences of the error? I don't know if the backup is successful despite the error.

I am using eDirectory 9.1.4.

Thank you in advance for your help.