TS-RVHL usb backup error

[sbertini88]

Hello all,
we have a problem with backup from nas share to usb disk on some files.
This is the error on log file produced on backup

amministra02/db_backup/mercoledi.bak
rsync: rename "/mnt/usbdisk4/amministra02/db_backup/.mercoledi.bak.5YqY12" -> "amministra02/db_backup/mercoledi.bak": Permission denied (13)

In the end of backup file we have this

rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1165) [sender=3.1.0]
-------- END BACKUP 2016/03/17 10:18:59 array1/mercoledi -> NAS@usbdisk4 --------

mercoledi.bak was not copied to usb disk but we don't understand what can cause this error?

Thanks

[davo]

Was the file in use at the time of the backup?

[sbertini88]

File was not in use.
It was copied to nas share at 10:00 PM.
Backup to usbdisk start next day at 10:00 AM