ORA-00955: name is already used by an existing object when creating a NEW materialized view

Hello:

I am using oracle 11.2.0.3 and trying to create a materivalized view as follows

CREATE MATERIALIZED VIEW RCUSER.VIEW_AUTHSUMMARY
  2    ORGANIZATION HEAP PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
  3    STORAGE(INITIAL 81920 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  4    PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
  5    TABLESPACE REQUESTCENTER
  6    BUILD DEFERRED
  7    USING INDEX
  8    REFRESH FORCE ON DEMAND
  9    USING DEFAULT LOCAL ROLLBACK SEGMENT
 10    DISABLE QUERY REWRITE
 11    AS SELECT TxA.ActivityID            AS ACTIVITYID,
 12         TxA.ClientOUID            AS OUID,
 13         TRUNC(TxA.DueOn)          AS DUEON,
 14         TRUNC(TxA.CompletedOn)    AS COMPLETEDON
 15    FROM TXActivity TxA
 16   WHERE TxA.ActivityTypeID       IN (2,3,11,12)
 17     AND TxA.StateID              IN (7,8,16,17,54,63,65)
 18     AND TxA.CreatorObjectID      IN (23,57)
 19     AND TxA.CompletedOn          >= TRUNC (ADD_MONTHS (SYSDATE,-7))