Below is what I think could be issue.

we see first error as 

PORT is not set, defaulting to 443
You may be taking backup of other VM using VCB if that is working fine then there is no issue with firewall on ESX server.

Now major issue we see here is

Mount point already exists for: d:\mnt\MOON.agios.local-fullVM
Exit Code: 19

The reason is after the sucessful backup the VM should be unmounted from VCB proxy server mount point.

Here seems this VM is left mounted on the mount point d:\mnt\ and when you run backup this fails.

Before runing a backup check on VCB proxy if the VM is in mounted in d:/mnt.

use vcbmounter command to unmount the VM on VCB proxy server.

once VM is unmounted you are ready to start the backup.

I hope this help .

Thank you Mukesh

I manually deleted the reference to the server in the mount directory on the

proxy server and that resolved the issue

Thank you

Tony