KB1857: Unable to allocate processing resources
https://www.veeam.com/kb185713.02.2014 · VERSION 7.X through to 9.X runs tasks in parallel, but can run sequentially with the parallel processing option disabled. Processing multiple disks on one VM will reserve multiple concurrent tasks. See Enabling Parallel Processing. Remember to not under-allocate your Veeam Backup server, especially if it is your backup proxy.