Sophos Anti-Virus: updates from CID fail and 'could not contact server' displayed on client computer

Issue
Your endpoint computers are not updating from the CID and AutoUpdate fails with 'Could Not Contact Server'. When you try to connect to the CID through Windows Explorer, there are no connection problems.

Sophos product and version
Sophos Anti-Virus, version 7 and above

Operating system
Windows XP Professional

What to do

1. On the client machine, check that the Workstation service is running.
   
   As described in Enterprise Console: remote task scheduling and installation on Windows 2000/XP/2003 computers (inglés), this service maintains a list of network connections for the system. If it is not started, those connections will be unavailable and the machine will not be able to update.
   
2. If this service is stopped, start it. If it is already started, stop and restart it.

Technical information

You may find the following error in the alc.log file:

Message: ERROR: Could not find a source for updated packages
Message: Could not connect to the server. Check that this computer is connected to the network and that Sophos AutoUpdate is configured to update from the correct location with the correct credentials and proxy details (if required)
Message: Could not add a connection to server \\<server>\InterChk; user domain1\savupdate; Windows error 5