Error setting file time

I have several million files on a system that I use UrBackup to backup from, and wanted to understand what file time is modified/changed on full file backups? (mtime/ctime/atime/all?)

Most of the logs have this warning which I’m not sure what permissions are required as they’re taking up real-estate rather that doing a storage file test and skipping from then onwards to save time.

WARNING Error setting file time of XXXXXXXXXXXXX Operation not permitted (code: 1)

I couldn’t find anything about file timestamp modification in 6.1 of the manual.

I’m using Debian as the server (to a network samba mounted drive 2gb+ NIC), which is backing up a local (separate NIC) Ubuntu client which has 3+ million files on a full backup. Both server and client aren’t being utilized during backup when logs repeatedly show this warning (CPU/storage = not even 20% used, and xfer ranges from 10kps 600kbps which is concerning even with ‘Run backups with background priority on the clients’ disabled )