, please adjust permission to the folder for Local System account under which you have the service started.
https://kb.cloudberrylab.com/standalone-backup/general/warning-one-or-more-backup-paths-do-not-exist

Thanks

is running as administrator domain

Getting the same thing - cloudberry creates the files, then gets access denied to them. It is running as Local Sysetm Account, The files it is backing up are via a share with share credentials provided.
Explicitly giving SYSTEM full access... will see if that works.

That is usually not required.
For local files simply enabling backup operators option is enough in most of the cases, changing service account is not necessary.

For network shares make sure that your network creds have full access to the files.
If that doesn't help try changing service account to administrator one.

If nothing helps - please create a ticket in our support system.