SQL & PL/SQL

Hi,
I am trying to run following query and i tried to run littel different way but no luck.
If someone can help me out.
I know that icann't use the alias in GROUP BY clause.
I am getting errors like "NOT a GROUP BY Function" or Identifier is not valid within my different fromat of the sql.
For C_CODE (MAx function part_, i have to make a header for each C__CODE and put the corrospondence value for S_TASK.


SELECT s_name ,login, f_name, l_name, email, S_ID, S_EMAIL,
desc, wave,

MAX(DECODE(C_CODE, '100',S_TASK, '')) "100",
MAX(DECODE(C_CODE, '150',S_TASK, '')) "150",
MAX(DECODE(C_CODE, '200',S_TASK, '')) "200"
FROM

*(*
SELECT b.S_name, d.login, d.f_name,d.l_name, d.email,
*(SELECT d.login FROM user d WHERE d.id = c.rep_to_id) AS S_ID,*
*(SELECT d.email FROM user d WHERE d.id = c.rep_to_id) AS S_EMAIL,*
e.desc, f.wave, C_CODE, S_TASK
FROM CT_E_STAK_MAP A,
ct_stak B,
e_info C,
user D,
e_code E,
e_web_info F,

C_STAK_MAP G,
C_CORS H,

C_S_TASK I,
C_S_STAK_MAP J
WHERE a.C_stak_id = b.c_stak_id

AND b.c_stak_id = G.c_stak_id
AND B.C_STAK_ID = J.C_STAK_ID
AND J.C_S_TASK_ID = I.C_S_TASK_ID
AND G.C_CORS_ID = H.C_CORS_ID
AND a.U_id = c.U_id

AND a.U_id = d.id

AND d.id = f.U_id

AND c.ctll3 = e.c_st_val

AND c.ctl1_2 = e.ctl1_2

AND e.c_set_name = 'EY'

AND c.active = 1
GROUP BY b.s_name, d.login, d.f_name,d.l_name, d.email,d.login, d.email, S_ID, S_EMAIL,
e.desc, f.wave, C_CODE, S_TASK
*)*
GROUP BY s_name ,login, f_name, l_name, email, S_ID, S_EMAIL, desc, wave

Please let me know if you need more info.
Thanks for your help!