Hi Ian,
The error message suggests that it can't establish a proper connection to the master file vault. Is the master vault online?
Does the client require a proxy to connect to that URL?
Are there any applications that could be interfering with the connection (i.e. firewall, single signon config settings on the server, etc.)?
If you have any WTDocuments stored in the master vault, do you have any trouble downloading those from a stand alone browser?