#1 Someone else is probably executing the package/procedure
while you are trying to delete it.
#2 you can find out who it is
by checking the view dba_lock_internal that can
be built using the catblock.sql script from the
$ORACLE_HOME/rdbms/admin directory - and
terminate their session if you can.
can u post the result of
SELECT sid||','||serial# username,
TO_CHAR(logon_time,'DD-MON-YY HH:MI: SSSS') loged_on
WHERE osuser = '<your operating system user>';