Have you examined the PBX log files found here C:\Program Files (X86)\VERITAS\VxPBX\log - there may be some additional clues in there.
The only thing that looks amiss in the logs is line:
PBX_Manager:pen, external IPV6 endpoint failed.,0:,2,(0|)
Not really sure what this is implying other than some kind of IPv6 issue
A couple of things to check:
When you deployed the client software, did you generate a certificate during setup, or skip that option? If PBX isn't connecting, I don't see how you could have setup the client during initial config.
Do you have IPv6 disabled in NetBackup? I ran into an issue similar to this with CloudCatalyst. We were able to set it up, everything worked fine, then we disabled IPv6 from the Admin Console and immediately starting having issues.