Unexpected end of SQl command error ORA-921

Question

I wrote this query as part of a larger query, however I can't seem to figure out why this ection gives me the ORA-921 error after the comparison expression (underlined below).
with
s2n as (
select distinct employeefk, policyref, advicename
from source
where
(payrollfk = (select payrollfk1 from payroll_1) or payrollfk = (select payrollfk2 from payroll_2)) and
displaysequence >= 0
group by employeefk, displaysequence, policyref, classificationtype, advicename, payrollfk)

Answer 1

I used hr demo tables for a similar query, check the usage examples of with clause - http://psoug.org/reference/with.html
C:\>sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Pzt Eyl 10 23:10:07 2007
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
SQL> conn hr/hr
Connected.
SQL> WITH tong AS (
  2    select distinct employee_id, first_name, last_name
  3    from employees
  4    where salary >= 0
  5          and (department_id = (select department_id from departments
  6                                   where department_name = 'IT') or
  7               department_id = (select department_id from departments
  8                                       where department_name = 'NOC')
  9              )
10    group by employee_id, first_name, last_name)
11  SELECT /*+ MATERIALIZE */ * FROM tong ;
EMPLOYEE_ID FIRST_NAME           LAST_NAME
        104 Bruce                Ernst
        105 David                Austin
        106 Valli                Pataballa
        103 Alexander            Hunold
        107 Diana                Lorentz