Failed to contact Netvault on Machine. Netvault must be active. (4046006)

Date: 7/07
Effected NV Version: NetVault Backup All
OS Version: All
Plugin version: NA
Application version: NA

Problem: Customer is able to add the Client in client management (right side only). But when making it an available client we get the familiar error: Failed to contact Netvault on Machine. NetVault must be active.

Solution:
Outside from the obvious: making sure that the Netvault processes are running on the client. And ablity to ping both ways IP and hostname, server to client, client to server. And telnet working both ways server to client, client to server.

Another thing to try that has helped me was to look in the /netvault/etc/machines.dat file and see how the Netvault Server lists the client information.
Then take this info in the Networking, Connection, and Preffered fields of this client and run the command nslookup with that info.

Example: nslookup 192.195.18.200
or nslookup scottk
I found in this customers case that nslookup could not find the machine from the Server. But the client was able to see the Server and other clients.

It turned out to be (hardware) Networking switch that was the culprit.