select TO_DATE ( 
TO_CHAR ( 
FROM_TZ ( 
   CAST ( 
      TO_DATE ( 
	 '2012-03-11 02:59:42', 
	 'YYYY-MM-DD HH24:MI:SS') AS TIMESTAMP), 
   'CST6CDT') 
   AT TIME ZONE 'Europe/Dublin', 
'YYYY-MM-DD'), 
'YYYY-MM-DD') dt 
from dual;

Gives error:
ORA-01878: specified field not found in datetime or interval

If i change the date part time from 02:59:42 to 03:59:42, it works fine without issues:

select TO_DATE ( 
TO_CHAR ( 
FROM_TZ ( 
   CAST ( 
      TO_DATE ( 
	 '2012-03-11 02:59:42', 
	 'YYYY-MM-DD HH24:MI:SS') AS TIMESTAMP), 
   'CST6CDT') 
   AT TIME ZONE 'Europe/Dublin', 
'YYYY-MM-DD'), 
'YYYY-MM-DD') dt 
from dual;

Gives output:
DT
3/11/2012

If i chnage the Hour part from 02 to any other number it works fine

select TO_DATE ( 
TO_CHAR ( 
FROM_TZ ( 
   CAST ( 
      TO_DATE ( 
	 '2012-03-11 03:59:42', 
	 'YYYY-MM-DD HH24:MI:SS') AS TIMESTAMP), 
   'CST6CDT') 
   AT TIME ZONE 'Europe/Dublin', 
'YYYY-MM-DD'), 
'YYYY-MM-DD') dt 
from dual;

Gives output:
DT
3/11/2012