I i've installed a fresh version of SEP SBE 12 but LiveUpdate wasn't able to download any updates. After some digging I discovered that update server lies about segment size (Content-Length says that segment size is 3584000 bytes while actual HTTP response body is only 3569664 bytes long). I found that an undocumented option DISABLE_SEGMENTED_DOWNLOADS can be used to circumvent the problem.
Just set PREFERENCES\DISABLE_SEGMENTED_DOWNLOADS=YES in Application Data\Symantec\LiveUpdate\settings.liveupdate.
Relevant info from log file is shown below.
04.01.2011, 16:38:03 GMT -> ProductRegCom/luGroup(PID=3292/TID=3312): Path for calling process executable is C:\Program Files\Symantec\LiveUpdate\luall.exe.
04.01.2011, 16:38:03 GMT -> ProductRegCom/luGroup(PID=3292/TID=3312): Destroyed luGroup object.
04.01.2011, 16:38:03 GMT -> Progress Update: PATCH_DOWNLOADING_START: Number of patches: 7
04.01.2011, 16:38:03 GMT -> GetUpdates: SESC Virus Definitions Win32 v11, MicroDefsB.CurDefs, SymAllLanguages ==> 1294151918jtun_nav2k8enncur25.m25
04.01.2011, 16:38:03 GMT -> GetUpdates: SESC Virus Definitions Win32 v11, MicroDefsB.Old, SymAllLanguages ==> 1292689975jtun_nav2k8ennful25.m25
04.01.2011, 16:38:03 GMT -> GetUpdates: SESC Submission Control Data, 11.0, SymAllLanguages ==> 1291246500jtun_the_scd.zip
04.01.2011, 16:38:03 GMT -> GetUpdates: SESC IPS Signatures Win32, 11.0, SymAllLanguages ==> 1293850291jtun_sescwps101231001.x86
04.01.2011, 16:38:03 GMT -> GetUpdates: Symantec Known Application System, 1.5.0, SymAllLanguages ==> 1222722077jtun_the_syknapps_engine.zip
04.01.2011, 16:38:03 GMT -> GetUpdates: Symantec Security Content B1, MicroDefsB.CurDefs, SymAllLanguages ==> 1294153784jtun_the_cal110104008.zip
04.01.2011, 16:38:03 GMT -> GetUpdates: Symantec Security Content A1, MicroDefsB.CurDefs, SymAllLanguages ==> 1294153648jtun_the_110104008.zip
04.01.2011, 16:38:03 GMT -> Progress Update: DOWNLOAD_BATCH_START: Files to download: 7, Estimated total size: 158569054
04.01.2011, 16:38:03 GMT -> Update file 1294151918jtun_nav2k8enncur25.m25 may be divided into bandwidth reducing segments.
04.01.2011, 16:38:03 GMT -> Progress Update: DOWNLOAD_FILE_START: URL: "1294151918jtun_nav2k8enncur25.m25", Estimated Size: 3584000, Destination Folder: "C:\Documents and Settings\All Users.WINXP\Application Data\Symantec\LiveUpdate\Downloads"
04.01.2011, 16:38:03 GMT -> Unable to find the property 'PREFERENCES\MAX_PACKAGE_SIZE' in settings file; using default: 734003200.
04.01.2011, 16:38:03 GMT -> HttpSendRequest (status 200): Request succeeded
04.01.2011, 16:38:22 GMT -> CstInetGetFile::DoHTTPTransfer - Unable to complete downloading a file from the server; err=12031.
04.01.2011, 16:38:22 GMT -> Progress Update: DOWNLOAD_FILE_FINISH: - NOTE - URL: "1294151918jtun_nav2k8enncur25.m25", Full Download Path: "C:\Documents and Settings\All Users.WINXP\Application Data\Symantec\LiveUpdate\Downloads\1294151918jtun_nav2k8enncur25.m25.seg1.zip" HR: 0x802A0046
04.01.2011, 16:38:22 GMT -> HR 0x802A0046 DECODE: E_UNABLE_TO_READ_DATA_FROM_SERVER
04.01.2011, 16:38:22 GMT -> Progress Update: DOWNLOAD_BATCH_FINISH: HR: 0x802A0046, Num Successful: 0
04.01.2011, 16:38:22 GMT -> HR 0x802A0046 DECODE: E_UNABLE_TO_READ_DATA_FROM_SERVER
04.01.2011, 16:38:22 GMT -> EVENT - SESSION END FAILED EVENT - The LiveUpdate session ran in Express Mode. LiveUpdate found 7 updates available, of which 0 were installed and 7 failed to install. The LiveUpdate session exited with a return code of 1835, ╤хЁтхЁ LiveUpdate эх юЄтхЄшы т Єхўхэшх Ёрчєьэюую яЁюьхцєЄър тЁхьхэш.
04.01.2011, 16:38:25 GMT -> LiveUpdate is about to execute a PostSession callback for product SESC Virus Definitions Win32 v11.
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=1928/TID=3692): Successfully created an instance of an luProductReg object!
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=1928/TID=3692): Path for calling process executable is C:\Program Files\Symantec\LiveUpdate\LuCallbackProxy.exe.
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=1928/TID=3692): Destroyed luProductReg object.
04.01.2011, 16:38:27 GMT -> The callback proxy finished executing the callback with a result code of 0x0
04.01.2011, 16:38:27 GMT -> The PostSession callback for product SESC Virus Definitions Win32 v11 completed with a result of 0x0
04.01.2011, 16:38:27 GMT -> Successfully released callback {855BA5F4-6588-4F09-AE61-847E59D08CB0}
04.01.2011, 16:38:27 GMT -> LiveUpdate has called the last callback for product SESC Virus Definitions Win32 v11, so LiveUpdate is informing the callback proxy that it can exit.
04.01.2011, 16:38:27 GMT -> LiveUpdate is about to execute a PostSession callback for product SESC IPS Signatures Win32.
04.01.2011, 16:38:27 GMT -> The callback proxy executable for product {C60DC234-65F9-4674-94AE-62158EFCA433} is exiting with no errors
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=3336/TID=3688): Successfully created an instance of an luProductReg object!
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=3336/TID=3688): Path for calling process executable is C:\Program Files\Symantec\LiveUpdate\LuCallbackProxy.exe.
04.01.2011, 16:38:27 GMT -> ProductRegCom/luProductReg(PID=3336/TID=3688): Destroyed luProductReg object.
04.01.2011, 16:38:27 GMT -> The callback proxy finished executing the callback with a result code of 0x0
04.01.2011, 16:38:27 GMT -> The PostSession callback for product SESC IPS Signatures Win32 completed with a result of 0x0
04.01.2011, 16:38:27 GMT -> Successfully released callback {855BA5F4-6588-4F09-AE61-847E59D08CB0}
04.01.2011, 16:38:27 GMT -> LiveUpdate has called the last callback for product SESC IPS Signatures Win32, so LiveUpdate is informing the callback proxy that it can exit.
04.01.2011, 16:38:27 GMT -> The callback proxy executable for product {D3769926-05B7-4ad1-9DCF-23051EEE78E3} is exiting with no errors
04.01.2011, 16:38:28 GMT -> *********************** End of LU Session ***********************