$sudo mv /mnt/disk/dir/* /mnt/disk/dir2/ Operation not allowed

Dear Community,

i moved to FreeNAS and enjoyed the encryption feature so far.
Now, i try to reorder my stuff in new ZFS Datasets. I tried to move over the shell files within on disk but somehow i am not allowed to do so as root. "Operation not allowed", "Permission error"

The dir has root:wheel.

I never saw such an error message with a root user
Could someone help me?

Thank you for your help.

best regards
JSunny