1898829 - Error during upgrade phase 'TR_CMDIMPORT_FDTASKS'

During an upgrade using the Software Update Manager (SUM), the phase TR_CMDIMPORT_FDTASKS terminates with the following error:

Log Name: SAPup.log
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
CURRENTPHASE PREP_EXTENSION/TR_CMDIMPORT_FDTASKS
...started at 20130809112123
# Using phase log file 'PCMDIMPFD.LOG'.
...begin processing at 20130809112132
..finished at 20130809112133 with status ABORTED.
# Error message set: 'Calling '/oracle/stage/up/SUM/abap/exe/tp' failed with return code 12, check /oracle/stage/up/SUM/abap/log/TP.ECO for details'
...begin dialog at 20130809112134
...end dialog at 20130809112816
..answered at 20130809112816.
-> decided to try again.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------

Log Name: TP.ECO
-----------------------------------------------------------------------------------------------
EXECUTING /oracle/stage/up/SUM/abap/exe/tp
pf=/oracle/stage/up/SUM/abap/var/PCMDIMP.TPP r3i all <SID>
This is tp version 380.05.18 (release 721, unicode enabled)
This is /oracle/stage/up/SUM/abap/exe/R3trans version 6.24 (release
720 - 08.07.13 - 20:13:05 ).
2EETW169 no connect possible: "maybe someone set invalid values for
DIR_LIBRARY ('/oracle/stage/up/SUM/abap/exe') or dbms_type
('ORA')"
/oracle/stage/up/SUM/abap/exe/R3trans finished (0012).
ERROR: stopping on error 12 during MAIN IMPORT
stopping on error 12 during MAIN IMPORT
-----------------------------------------------------------------------------------------------

SAP Netweaver

TR_CMDIMPORT_FDTASKS; Upgrade; SUM; kernel; tp; R3trans; TP.ECO; 2EETW169; connect; possible; invalid; DIR_LIBRARY; dbms_type; , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , Problem