During client backup, some of them fail with log error messages:
- machine xxx Changed it's preferred address from xxx.. to xxy..
- Machine xxx has gone down
- Cannot gain network access to client machine
- Failed to start plugin
- Backup Failed
The message "changed it's preferred address from 10.. to 10..." suggests that the NetVault server or the clients concerned have more than one interface.
Multiple NICs on machines that need to establish a durable connection for streaming data can lead to confusion when the NIC to be used is not specified.
On the machine(s) that possess multiple NIC (or multihomed/several IPs), we need to specify the Preferred Network address that will always be used
and bar the one(s) we won't be using.
For this to happen do the following:
 Go to the server's nvconfigurator | Network Manager | Connections | and specify the Preferred Network Address | but also specify the one(s) to be barred (Comma separated list of barred addresses).
 On server as well as client(s) (ALL machines involved), Stop the services and delete each machines.dat files. You will find them under /Netault/etc.
 Start the NetVault services and wait at least 10 minutes to allow the new machines.dat files to be recreated while discovering the new network changes.
This is because the Availibility broadcasts occur every 5 minutes.
Note that if the client has also multiple NICs step  should also be done on the client as well.