Why does plsql give compilation error for select statement?

Question

When I run following plsql program, it gives compilation error. Could somebody please point me out what could be wrong here? I am running it from system user.
create or replace procedure drop_user_proc (iname in varchar2) is
uname varchar2(100);
begin
select username into uname from dba_users where username = upper(iname);
end drop_user_proc;
select username from dba_users where username = upper('newuser');
When I run it, I get following error. dba_users is there that is the reason it works outside plsql block, but it doesn't from inside block.
SQL> @t4
Warning: Procedure created with compilation errors.
USERNAME
NEWUSER
SQL> show err
Errors for PROCEDURE DROP_USER_PROC:
LINE/COL ERROR
4/3 PL/SQL: SQL Statement ignored
4/35 PL/SQL: ORA-00942: table or view does not exist

Answer 1

Role based grants are not available within the stored procedures.
Only explicit grants are recognized when compiling stored code.
You need to grant select on that table to the user where you are creating this procedure.