No host name entry for the virtual machine exists in the DNS server or in the Windows hosts file on the Hyper-V server:

Windows\System32\drivers\etc\hosts

Create a virtual machine name entry in either the DNS server or in the hosts file of the Hyper-V server.

A firewall is enabled and no port entry exists for the primary server.

Add a port entry for the NetBackup primary server.

See the NetBackup Administrator's Guide.