When performing a backup, the backup client displays an error "Invalid sync token found - ensure this is the only backup client backing up to this account".
A similar error will be seen on the Storage Platform as well: "Warn: GROUP\ACCOUNT - Backup: Sync tokens do not match. User possibly backing up from a different machine."
Every time a backup completes, a unique value is stored on both the backup client and the StorageServer. This value is sent from the backup client to the StorageServer on the next backup as part of the verification process. When this token does not match, it means that the last known backup does not match between the backup client and the StorageServer.
The following are typical scenarios when the error is seen:
When reconnecting to an account, e.g. after a reinstall of the backup client. There will be no token present on the backup client.
Perform a backup. After a successful backup completion, the token will be updated.
There was a problem on the backup client updating the cache (or the cache is corrupt/has been cleared).
Check the backup logs and resolve any issues that can cause problems during the cache update. Once resolved, perform a backup. After a successful backup, the token will be updated.
More than one machine backing up to the same account.
This can be spotted in the AccountServer or StorageServer logs. As seen in the example below, the backup comes from two different IPs and operating systems while the group and account names are the same.
00:00:24.599 (25) Info: GROUP\ACCOUNT- ASCommsManager: Backup client backup request from 172.23.0.33 (Type=SE, Version=220.127.116.113, Service Pack=0, Brand=A5BP, OS=Windows 2008)
02:56:40.097 (42) Info: GROUP\ACCOUNT - ASCommsManager: Backup client backup request from 172.23.0.34 (Type=SE, Version=18.104.22.1683, Service Pack=0, Brand=A5BP, OS=Windows 2003)
Note: The IP is not always a valid indicator, as the IP can change if a client is mobile or multi-homed. Also IPs may even be identical if the duplicate clients both sit behind a NAT router. If a NAT router is present, it may be necessary to check the NAT session table to locate the original IP addresses.
Another indicator can be the backup client version or OS. However, note that the OS may appear identical. A common cause of this problem is a cloned Virtual Machine where the client has been installed previously.
Note: Data corruption can occur in this scenario, resulting in errors and large backups daily, as well as the inability to restore data.
Regardless of how the problem has occurred, the error will persist until the duplicate client is prevented from backing up.
Remove the backup client from the additional machine(s) or create new backup accounts and run a full integrity check on the affected account.