ERROR: client not validated to perform requested operation

Extract from NBU Exchange Admin Guide :

To configure privileges for granular clients and clients in virtual environments
1 On the master server, create the altnames directory, as follows:
■ In a non-clustered environment, create the following directory:
install_path\NetBackup\db\altnames
■ In a clustered environment, create the following directory:
shared_drive_install_path\NetBackup\db\altnames
2 In the altnames directory, create a peername file.
Peername is the name of the proxy host or off-host client. For clustered clients, create a peername file for each node in the cluster. For a 2010 DAG, create one file for each physical Exchange server in the DAG.
For example, consider that you have a source client named ClientA and you want to use a proxy host named ProxyClient. On the master server, you create a file that is called proxyclient.
3 In the peername file, add the name of the source client.
The source client is the client that originally performed the backup. For clustered clients, use the virtual Exchange name. For a backup within a private network, use the private network host name. For a DAG, use the DAG name; this name should be the client name in the policy.
For example, in the proxyclient, include the name clienta.