Central Monitoring Problem

[GlennB]

I have a machine that reports the following error when it tries to connect to the Central Monitoring Server.

JobComplete message could not be sent for job execution 1.328 with result Exception. Retrying later. Message: Network error when connecting to BackupAssist Central Monitoring Server:
The remote server returned an error: (417) Expectation failed.
Check your Internet connection and firewall settings.

I have check the internet connection and it is working ok, connection to the BackupAssist website from the machine works ok.
If I try and deregister the machine from Centralized monitoring then it reports

Network error when connecting to BackupAssist Central Monitoring Server:
The remote server returned an error: (417) Expectation failed.
Check your Internet connection and firewall settings.

Has anyone seen this issue before ?
(Machine is running version 6.1.1)