ORA-29855 creating the Oracle Text Context index based on a clob field

Hi Friends,

When I create the Oracle Text Context index based on a clob field (Audit Vault Server - event_log table  command_text field), I gets the following errors

create index myindex on event_log(command_text_clob) indextype context

parameters('memory 1G')

-------------------- Error -----------------------

[Error] Execution (4: 1): Error: ORA-29855: error occurred in the execution of ODCIINDEXCREATE routine

ORA-20000: Oracle Text error:

DRG-50857: oracle error in drvddl.IndexCreate

ORA-20000: Oracle Text error:

DRG-50857: oracle error in drekr2kFlush (execute insert)

ORA-30036: unable to extend segment by 8 in undo tablespace 'UNDOTBS'

ORA-06512: konum "CTXSYS.DRUE", satır 160

ORA-06512: konum "CTXSYS.TEXTINDEXMETHODS", satır 366