Backup fails with "Selected network files or network folders were not found: <NETWORK PATH>"
You are backing up files or folders on a network share and these files/folders are not available.
From the error message, note which files/folders could not be found.
Verify that these files/folders still exist and are accessible for Acronis Agent. Possible root causes could be:
Items have been moved/deleted. Specify new location in the backup plan or remove them from items to back up.
Items have been renamed. Re-select these items in the backup plan.
Share is no longer accessible. Make sure the folders are still shared (right-click -> Properties -> Sharing -> Share -> make sure the folder is shared and is accessible for everyone or Administrators/Acronis Agent user specifically).