unable to open file - Read-only file system

[Clburnier]

Hi, I have a problem for Backup my VM, I use a Open Media Vault VM with a NFS share as Backup storage, but when i want to backup, i have this error.
ERROR: unable to open file '/mnt/pve/Backup/dump/vzdump-qemu-102-2023_12_07-13_34_38.vma.dat' - Read-only file system
When i try to chmod the "Backup", i have this message.

Can you help me ?