SQL & PL/SQL

hi , i am using oracle 10g db , and i am trying to kill all sessions connected to the database with this code :

CREATE OR REPLACE PROCEDURE kill_sessions IS 
begin     
    for x in (  
            select Sid, Serial#, machine, program  
            from v$session  
            where  
                username <> 'the one i am connected to in order to kill sessions' 
        ) loop  
        execute immediate 'Alter System Kill Session '''|| x.Sid  
                     || ',' || x.Serial# || ''' IMMEDIATE';  
    end loop;  
end;

when i issue this code from a user which i granted the DBA privilege to him , i face these errors :

but when i log on with " sys as sysdba " , the procedure is created successfully without any errors .

do i miss something here ? do i need any other privileges other than the " DBA " one ?

thanks a lot