Problema com INSERT

[Anônimo]

tente substituir :
(select titulo_seq.nextval from dual)

por: titulo_seq.nextval

veja:
SQL> create sequence test ;

Sequence created.

Elapsed: 00:00:00.01
SQL> create table tab2( campo number, nome varchar2(10)) ;

Table created.

Elapsed: 00:00:00.02
SQL> insert into tab2 values( test.nextval, ‘ABC’) ;

1 row created.

Elapsed: 00:00:00.01
SQL>