Sophos could not contact server

I have got Sophos Antivirus version 7.3.4 .

 I never had problem supdating it but today, it shows the following error message

'Sophos could not contact server'

Log files shows the following errors:

Trace(2014-Apr-04 18:53:15): ALUpdate started: -ManualUpdate -NoGUI -RootPath "C:\Program Files (x86)\Sophos\AutoUpdate"
Trace(2014-Apr-04 18:53:15): Product subscription is disabled: iProductData.{390DCDC2-10A9-4ef3-B8D8-0CA7F0E7EB92} action value is:0
Trace(2014-Apr-04 18:53:15): Product iProductData.{390DCDC2-10A9-4ef3-B8D8-0CA7F0E7EB92} has not been added.
Trace(2014-Apr-04 18:53:15): Product subscription is disabled: iProductData.{D752FAB9-5883-4b36-8740-61565B6BAD29} action value is:0
Trace(2014-Apr-04 18:53:15): Product iProductData.{D752FAB9-5883-4b36-8740-61565B6BAD29} has not been added.
Trace(2014-Apr-04 18:53:15): Product iProductData.{E17FE03B-0501-4aaa-BC69-0129D965F311} has been added.
Trace(2014-Apr-04 18:53:15): Product iProductData.{E17FE03B-0501-4aaa-BC69-0129D965F311} is available from Sophos.
Trace(2014-Apr-04 18:53:15): Product iProductData.{E17FE03B-0501-4aaa-BC69-0129D965F311} is not the Spam Rules package.
Trace(2014-Apr-04 18:53:15): Product subscription is disabled: iProductData.{7998C326-2CA5-4830-B7D2-B792D2460975} action value is:0
Trace(2014-Apr-04 18:53:15): Product iProductData.{7998C326-2CA5-4830-B7D2-B792D2460975} has not been added.
Trace(2014-Apr-04 18:53:15): Product iProductData.{3B758ED7-87C1-4e89-BDE1-F49DFF1249F6} has not been added.
Trace(2014-Apr-04 18:53:15): Product iProductData.{B5E7E2A7-3B64-437D-801F-21CC9D67CC6D} has been added.
Trace(2014-Apr-04 18:53:15): Product iProductData.{B5E7E2A7-3B64-437D-801F-21CC9D67CC6D} is available from Sophos.
Trace(2014-Apr-04 18:53:15): Product iProductData.{B5E7E2A7-3B64-437D-801F-21CC9D67CC6D} is the Spam Rules package.
Trace(2014-Apr-04 18:53:15): ConfigurationImpl, considering PMSR: PureMessage not installed, PMSR package will not be updated
Trace(2014-Apr-04 18:53:15): Considering subscribed products.
Trace(2014-Apr-04 18:53:15): Considering product {9BF40A4E-23AE-48be-9974-5A1F261DBEE8}
Trace(2014-Apr-04 18:53:15): Product {9BF40A4E-23AE-48be-9974-5A1F261DBEE8} is not already subscribed.
Trace(2014-Apr-04 18:53:15): Product {9BF40A4E-23AE-48be-9974-5A1F261DBEE8} was added to the list.
Trace(2014-Apr-04 18:53:15): Considering product {E17FE03B-0501-4aaa-BC69-0129D965F311}
Trace(2014-Apr-04 18:53:15): IPCBase::IPCBase: Initialising shared memory A32951C539924a12B3C8F2FDA5A268E4
Trace(2014-Apr-04 18:53:15): IPCSender::ProcessSend started
Trace(2014-Apr-04 18:53:15): IPCSender::ProcessSend: No messages in queue, starting to wait
Trace(2014-Apr-04 18:53:15): RMSMessageHandler: ALUpdateStart
Trace(2014-Apr-04 18:53:15): IPCSender::Write: Writing message: <?xml version="1.0" encoding="utf-8" ?><Config type="RMSStartUpdate" />
Trace(2014-Apr-04 18:53:15): IPCSender::ProcessSend: Send message: <?xml version="1.0" encoding="utf-8" ?><Config type="RMSStartUpdate" />
Trace(2014-Apr-04 18:53:15): IPCSender::ProcessSend: No messages in queue, starting to wait
Trace(2014-Apr-04 18:53:15): ALUpdate(AutoUpdate.Started):
Trace(2014-Apr-04 18:53:15): UpdateCoordinator::UpdateNow: Entering
Trace(2014-Apr-04 18:53:15): PopulateCache: Entering
Trace(2014-Apr-04 18:53:15): UpdateCoordinator::UpdateNow: About to Sync list of products
Trace(2014-Apr-04 18:53:15): UpdateLocationFacade::SyncProduct: Last Update Mechanism = Unknown
Trace(2014-Apr-04 18:53:15): TrySyncProduct<class AutoUpdate::SDDSUpdateLocation>, Started:
Trace(2014-Apr-04 18:53:15): TrySyncProduct<class AutoUpdate::SDDSUpdateLocation>, creating update location
Trace(2014-Apr-04 18:53:15): Path to decode files to: C:\Windows\TEMP\sophos_autoupdate1.dir\1396633995
Trace(2014-Apr-04 18:53:15): Using top level catalogue sdds.xrsesc
Trace(2014-Apr-04 18:53:15): SDDSUpdateLocation, constructor start
Trace(2014-Apr-04 18:53:15): locConfig.m_server = http://es-web.sophos.com/update/
Trace(2014-Apr-04 18:53:15): Calling check on source.m_address.m_path = http://es-web.sophos.com/update/
Trace(2014-Apr-04 18:53:15): Calling package_source_init
Trace(2014-Apr-04 18:53:15): Creating HttpPackageSource
Trace(2014-Apr-04 18:53:15): Composite upstream PSN: {root|http://es-web.sophos.com/update/|****:****}{mapped|{file|C:\ProgramData\Sophos\AutoUpdate\data\warehouse|}{f_translate}{file|C:\ProgramData\Sophos\AutoUpdate\data\warehouse|}|}
Trace(2014-Apr-04 18:53:15): CreatingFilePackageSource
Trace(2014-Apr-04 18:53:15): Local PSN: {file|C:\ProgramData\Sophos\AutoUpdate\data\warehouse|}{f_translate}{file|C:\ProgramData\Sophos\AutoUpdate\data\warehouse|}
Trace(2014-Apr-04 18:53:15): SDDSUpdateLocation::Constructor finished
Trace(2014-Apr-04 18:53:15): TrySyncProduct, Calling BeginSync
Trace(2014-Apr-04 18:53:15): SDDSUpdateLocation caught exception from BeginSync: Connection dropped while downloading http://es-web.sophos.com/update/catalogue/sdds.xrsesc.xml downloaded 1064 bytes of 0
Trace(2014-Apr-04 18:53:15): TrySyncProduct<class AutoUpdate::SDDSUpdateLocation>, Ended - 0
Trace(2014-Apr-04 18:53:15): TrySyncProduct<class AutoUpdate::CIDUpdateLocation>, Started:
Trace(2014-Apr-04 18:53:15): TrySyncProduct<class AutoUpdate::CIDUpdateLocation>, creating update location
Trace(2014-Apr-04 18:53:15): Calling package_source_init
Trace(2014-Apr-04 18:53:15): TrySyncProduct, Calling BeginSync
Trace(2014-Apr-04 18:53:16): ALUpdate(Error):
Trace(2014-Apr-04 18:53:17): IPCSender::ProcessSend exiting
Trace(2014-Apr-04 18:53:17): ALUpdate::main: terminal problem!