zac reg fails "Exception: Failed to read from an IPC Port"

Performing workstation builds using the ENGL Imaging Toolkit build process (v8.01)

We have one workstation where the 'zac reg' failes after 20mins with the
"Exception: Failed to read from an IPC Port: The pipe has been ended.
UnableToCommunicateRemotingError"

From the wstn zmd-messages you get
Registration successful, response was '' (i.e. null)

and in the server services-messages there are iterative " [DEBUG] [13/01/14 16:05:39] [] [Registration Web Service] [104] [] [refreshing ignored list of reconcile attributes] [] []
[DEBUG] [13/01/14 16:05:39] [] [Registration Web Service] [104] [] [registerDevice complete, time: 94ms, code: 0, device: 7d8390f3945b5f4ead1cf844f25fcf6e, thread: 104] [] []"

I see this on whichever primary server I point the device at (have tried two)

I have tried clearing zisd, I have tried updating and resetting BIOS, I have tried a replacement hard disk.
I have tried forcing registration to a different primary (same result)

I am wondering whether there is a 'bad' record in the database relating to this device, however I have performed ZCM queies on serial number, etc. and can't see anything...

Has anyone seen this type of error? or can suggest additional troubleshooting?

Thanks

David