logminer issues

i tried to recover a table using logminer as follows :

SQL>begin
dbms_logmnr.start_logmnr (
starttime => '9-jan-2013 11:00:00',
endtime => '9-jan-2013 11:00:00,
options => dbms_logmnr.dict_from_online_catalog +
dbms_logmnr.continuous_mine +
dbms_logmnr.no_sql_delimiter +
dbms_logmnr.print_pretty_sql
);
end;
/

but when i selected from v$logmnr_contents its giving me "UNKNOWN" username and os_username.

any ideas why ?