SQL & PL/SQL

Hi ,
I have created successfully some months ago some MV. Later on , I was made to destroy the database and create a new one , using the DBCA. The peculiar is that whenever i issue the command :
sql> drop materialized view stat_biox_f_mv;

Oracle displays the error ORA-12003: the materialized view stat_biox_f_mv does not exist.

When i issue the command:
sql>create materialized view stat_biox_f_mv
build immediate
refresh start with (sysdate)+(10/1440)
next (sysdate)+10/1440
as
select count(f) N_f,sum(f) Sx_f,round(avg(f),3) x_f,round(stddev(f),3) SD_f,
round(avg(f)+2*stddev(f),3) Ru_f,round(avg(f)-2*stddev(f),3) Rd_f,
round(stddev(f)/sqrt(count(f)),3) SE_f,round((100*stddev(f))/avg(f),3) CV_f,
round(count(f)*((sum(power(f,4))-(power(sum(f),4)/count(f)))/
(power((sum(power(f,2))-(power(sum(f),2)/count(f))),2)))-3,3) Sk_f,
round((sum(power(f,2))-(power(sum(f),3)/count(f)))/
(power(stddev(f),2)*count(f)),3) Sa_f
from biox
/

Oracle displays the error ORA-00955: the object does exist

Eventually , the object exists or does not...?????

Thanks , a lot
Simon