Cannot connect to Data Protector Express Storage Domain

[Fisheye Support]

Here's my config

ML350G5 with HP Ultrium 920 SAS Tape drive.
O/S is Windows 2008 Server Core x64 Standard edition running the Hyper-v Role.

Running in the Virtual Environment is SBS 2003 R2 Premium.

Both O/S have HP Data Protector Express installed.

I cannot get either server to join the others storage domain.
Both machine can ping each other.
When I attempt to join the Server ore storage domain I can see the outbound traffic in ISA server on port 3817.
When I attempt the reverse (from 2008 to SBS) it fails much faster and I see no traffic in ISA.
I've tried enabling port 3817 in the 2008 firewall for traffic in both directions without success.
The error is the same on both installs -
code 129(0x81) Unable to connec to primary Domain Server instance.