Your backup service works under your Local System account, but I assume that you connect to your NAS box using done other credentials.
You either should:
1. Connect to your NAS after adjusting permissions on your NAS to connect from this computer (local system account is the same as a computer account). https://kb.cloudberrylab.com/standalone-backup/general/warning-one-or-more-backup-paths-do-not-exist
Start with section 5.
2. Start you backup service under the same user that you use to connect to your NAS.
Should also note that the backup is also to the NAS
Hi Anton, thank you for your reply, I've created a local user with the same name and permissions as the NAS account and the ISO was successfully created. Thanks again!