Backup source does not exist ! or Skip backing up (network drive is not accessible) "\\xxx.xxx.xxx.xxx\folder name"

Error

When a scheduled backup runs and the data source is another device on the network with a UNC pathname, you might see an error similar to these error messages below:

Backup source “\xxx.xxx.xxx.xxx\folder” does not exist !
Skip backing up “\xxx.xxx.xxx.xxx\folder” (network drive is not accessible)
Normally these connections are NAS devices.

It is probable manual backups have worked without issue.

Cause

When you run a manual backup, the credentials of the logged-on user on Windows are used.
Because the Windows account can access the NAS over the network, the backup will also be able to connect to the NAS device because it is running with the same permissions.

When a scheduled backup runs, the scheduler service (Desktop Services or Server Services) will use the default Windows account which is the Local System account.

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This is the default built-in system account which Windows services use. It will have access to all local and unmodified resources but won’t have sufficient permissions to access NAS and other UNC devices unless they are Active Directory enabled.

Fix

Change the user account running under the service (Desktop Services or Server Services) to the same as the logged-in Windows user which can run a manual backup or one which has permissions to access the device on the UNC path.