PL/SQL :: Error When Creating A Table / ORA-00957 - Duplicate Column Name

I'm getting an error as follows .

create table asgnd_agent_bak as (Select * from ASGND_AGENT a, SCN s
where
a.CNTCT_KEY = s.CNTCT_KEY and a.SCN_NUM=s.SCN_NUM
and a.ACTVTY_DT = to_date('03/17/2013','mm/dd/yyyy')
and s.SCN_OPEN_DT = to_date('03/15/2013','mm/dd/yyyy')
and a.SRC_SYS_DESC = 'FACET');
create table asgnd_agent_bak as (Select * from ASGND_AGENT a, SCN s
*
ERROR at line 1:
ORA-00957: duplicate column name