A known issue exists in the Enterprise Server Edition Backup Client when authentication credentials are enabled for a backup selection on a network folder (in the Backup Selection tab's Network view).
The problem occurs when said credentials are changed to a different user, resulting in the previous user's file selection being displayed.
This is because, even though the Backup Client requests that the connection made by the previous "user" be closed, the Windows operating system has not actioned it yet.
The issue is known to Microsoft but as yet no fix has been released.
We recommend waiting approximately 10 minutes before trying again.