Appliance media server - certificate issue

I have a media server 3.1.2 connected to a master server 8.1.2 (linux) and the appliance is offline in the media management.

Looking the vxlogview on master, I'm seeing this message:

The peer proxy on host (mediaserver ) failed to find usable certificates. Certificates may not have been successfully deployed., nbu status = 7660, severity = 2, Additional Message: [PROXY] Encountered error (CERT_PROTOCOL_SELECT_COMMON_CA_ROOT) while processing(CertProtocol)., nbu status = 4, severity = 1"} vnet status: 7660

So, I went to the master server and the certicate seems ok (Active). Looking the documentation, I should run on media server nbcertcmd -getCACertificate, but how can I do it from Netbackup Appliance?