OpenVZ backup error

[decibel83]

Hi.
When I try to backup an OpenVZ virtual machine I get these errors:

Sep 21 15:09:09 INFO: Starting Backup of VM 306 (openvz)
Sep 21 15:09:09 INFO: CTID 306 exist mounted running
Sep 21 15:09:09 INFO: status = running
Sep 21 15:09:09 INFO: mode failure - unable to detect lvm volume group
Sep 21 15:09:09 INFO: trying 'suspend' mode instead
Sep 21 15:09:09 INFO: backup mode: suspend
Sep 21 15:09:09 INFO: ionice priority: 7
Sep 21 15:09:09 INFO: starting first sync /mnt/pve/data/private/306/ to /mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/console" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/full" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/kmem" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop0" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop1" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop2" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop3" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop4" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop5" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop6" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/loop7" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/mem" failed: Permission denied (13)
Sep 21 15:09:11 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/dev/null" failed: Permission denied (13)

... Some other similar errors ...

Sep 21 15:11:20 INFO: rsync: mknod "/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp/var/spool/postfix/dev/urandom" failed: Permission denied (13)
Sep 21 15:11:20 INFO: Number of files: 49261
Sep 21 15:11:20 INFO: Number of files transferred: 38601
Sep 21 15:11:20 INFO: Total file size: 1783049573 bytes
Sep 21 15:11:20 INFO: Total transferred file size: 1782576681 bytes
Sep 21 15:11:20 INFO: Literal data: 1782576681 bytes
Sep 21 15:11:20 INFO: Matched data: 0 bytes
Sep 21 15:11:20 INFO: File list size: 1160249
Sep 21 15:11:20 INFO: File list generation time: 0.020 seconds
Sep 21 15:11:20 INFO: File list transfer time: 0.000 seconds
Sep 21 15:11:20 INFO: Total bytes sent: 1785624439
Sep 21 15:11:20 INFO: Total bytes received: 771040
Sep 21 15:11:20 INFO: sent 1785624439 bytes  received 771040 bytes  13584756.49 bytes/sec
Sep 21 15:11:20 INFO: total size is 1783049573  speedup is 1.00
Sep 21 15:11:20 INFO: rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1070) [sender=3.0.9]
Sep 21 15:11:41 ERROR: Backup of VM 306 failed - command 'rsync --stats -x --numeric-ids -aH --delete --no-whole-file --inplace '/mnt/pve/data/private/306/' '/mnt/pve/backup/dump/vzdump-openvz-306-2015_09_21-15_09_09.tmp'' failed: exit code 23

This virtual machine is stored on a NFS storage and I'm trying to backup it saving the dump on another NFS storage.
If I try to dump to the local storage, I don't get any error and dump works.

Could you help me please?

Thank you very much for your help!
Bye