Error Message:

The specified path has already been added.

Explanation:

You have entered a duplicate path name for backing up the Account Synchronization Database. There should be a path to one or more computers where the database will be copied. It is recommended that at one of the two backup paths point to the \systemroot\SYNCAGNT\BACKUP directory on the Backup Domain Controller (BDC). This simplifies the steps necessary to promote the BDC to a PDC in case the PDC becomes unavailable.

User Action:

If you have already designated a backup path on the Primary Domain Controller, then edit the path name to create a hidden share named \\server_name\DSMN$ that points to the \%systemroot%\SYSTEM32\SYNCAGNT directory on the backup domain controller.