ORA-38881: Cannot drop tablespace

SQL> drop tablespace aud_aux including contents and datafiles;
drop tablespace aud_aux including contents and datafiles
*
ERROR at line 1:
ORA-38881: Cannot drop tablespace AUD_AUX on primary database due to guaranteed
restore points.


SQL> SELECT NAME, SCN, TIME, DATABASE_INCARNATION#,        GUARANTEE_FLASHBACK_D
ATABASE,STORAGE_SIZE        FROM V$RESTORE_POINT;

NAME
--------------------------------------------------------------------------------

       SCN
----------
TIME
---------------------------------------------------------------------------
DATABASE_INCARNATION# GUA STORAGE_SIZE
--------------------- --- ------------
SWITCHOVER_START_GRP
   1518415
13-JAN-14 02.07.10.000000000 PM
                    4 YES    629145600


SQL> drop restore point switchover_start_grp;

Restore point dropped.

SQL> drop tablespace aud_aux including contents and datafiles;

Tablespace dropped.

SQL>