1948943 - Error in upgrade phase "PREP_IMPORT/SQLDB_CLEARPATCHES"

During the upgrade, Software Update Manager (SUM) stops in phase PREP_IMPORT/SQLDB_CLEARPATCHES with error message as below :

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EXECUTING <SUM Directory>\abap\exe\tp.EXE "pf=<SUM Directory>abap\var\DEFAULT.TPP" execdbscript APD -x ..\var\SQLDBSCRIPT.TQL
This is <SUM Directory>\abap\exe\tp.EXE version 380.08.41 (release 720, unicode enabled)
TRACE-INFO: 1: [ dev trc,00000] Wed Nov 27 13:18:41 2013 193429 0.193429
TRACE-INFO: 2: [ dev trc,00000] DlLoadLib success: LoadLibrary("dbmssslib.dll"), hdl 0, addr 000007FEEF380000
TRACE-INFO: 3: 10 0.193439
TRACE-INFO: 4: [ dev trc,00000] using "<SUM Directory>\abap\exe\dbmssslib.dll" 7 0.193446
tp returncode summary:
TOOLS: Highest return code of single steps was: 0
ERRORS: Highest tp internal error was: 0249
tp finished with return code: 249
meaning:
connect failed due to DbSL load lib failure
tp=>sapparam(1c): No Profile used.
tp=>sapparam: SAPSYSTEMNAME neither in Profile nor in Commandline
ERROR: No connect due to DbSl Load Lib Failure
ERROR: Possible reasons are:
ERROR: - The value set for dbms_type ('mss') is invalid.
ERROR: - Cannot find the DLL dbmssslib.dll in path
ERROR: - problems when loading DB-dependent DLLs
ERROR: Connect to APD failed (20131127131841).
SAPup> Process with PID 8256 terminated with status 249 at 20131127131841!
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Software Update Manager

SQLDB_CLEARPATCHES, SUM, Upgrade, execdbscript, SQLDBSCRIPT.TQL, 0249, DbSL, load, lib, failure, dbms_type, dbmssslib.dll, non-unicode, unicode, kernel, database; , KBA , BC-UPG-PRP , Upgrade Preparation , BC-UPG-TLS-TLA , Upgrade tools for ABAP , Problem