Management Server Connection Failed

SEC 9.7 and database running on a Windows 2003 server. We upgraded from 9.5 to 9.7 about 6 weeks ago.

The SEC 9.7  I run on my desktop had been running OK until Monday this week when it crashed mid-morning. I rebooted the server and was able to start my SEC again OK.  Shut my desktop machine down Monday evening and after I restarted it Tuesday morning found that neither myself nor others who also run an SEC from their desktops could run a SEC. It also fails when I log onto the server and try. A further reboot of the server hasn't fixed it.

If one tries to start up the SEC one gets the usual "Connecting to server, might take a few seconds" message which after a while changes to a window entitled "Management Server Connection Failed"  saying that it "Could not connect to the Management server" and listing some possible reasons.

Looking in the event log I see entries about the Sophos Management Service failing:

Application log event 8004 (this is type Error):

Initialization
failed.

Step:
Creating a database connection

Error:
std::runtime_error

Data:
createAccessToken: LogonUser failed

and in the System log three events:

7023 (this is type Error):

The
Sophos Management Service service terminated with the following error:

Unspecified
error

For
more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Followed by

7035 (this is type Information):

The Sophos Management Service service was successfully sent a start control.

For
more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

7036
(this is type Information):

The
Sophos Management Service service entered the stopped state.

For
more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Looking at the services running on the server I see that the Sophos Management Service shows as startup type automatic but isn't started.

Trying to start it by hand generates a window  "Windows could not start the Sophos Management Service on [name of server]"

error 0x80004005: Unspecified error

and there's a matching 8004 error entry in the event log:

Initialization failed.

Step: Creating a database connection

Error: std::runtime_error

Data: createAccessToken: LogonUser failed

Any ideas on where to look for the underlying cause of the problem please? 

Could "createAccessToken: LogonUser failed" maybe relate to an account that the service was using having had its password changed? But then how to find where the account is specified and to change it?

Thanks for any help.