When trying to enable “FND: Debug Log Enabled”, in the below window, it might sometime be that the option to set it to Yes/No, is grayed out, and cannot be changed. Without spending too much time fixing this, you can also enable/disable it from within a sqlplus session, connected as the apps user.
To enable it, do the following
SQL> SELECT PROFILE_OPTION_ID,PROFILE_OPTION_NAME FROM FND_PROFILE_OPTIONS_VL
WHERE START_DATE_ACTIVE <= SYSDATE
and NVL(END_DATE_ACTIVE,SYSDATE) >= SYSDATE
and ( SITE_ENABLED_FLAG = ‘Y’ or APP_ENABLED_FLAG = ‘Y’ or RESP_ENABLED_FLAG = ‘Y’ or USER_ENABLED_FLAG = ‘Y’ or SERVER_ENABLED_FLAG = ‘Y’ or SERVERRESP_ENABLED_FLAG = ‘Y’ or ORG_ENABLED_FLAG = ‘Y’)
and ( UPPER(USER_PROFILE_OPTION_NAME) LIKE ‘%FND%DEBUG%’
and (USER_PROFILE_OPTION_NAME LIKE ‘%f%’ or USER_PROFILE_OPTION_NAME LIKE ‘%F%’))
order by user_profile_option_name;
PROFILE_OPTION_ID PROFILE_OPTION_NAME
—————– ———————————–
             4176 AFLOG_ENABLED
             3098 AFLOG_FILENAME
             3099 AFLOG_LEVEL
             8470 AFLOG_BUFFER_MODE
             3100 AFLOG_MODULE
             8468 DEBUG RULE THRESHOLD
6 rows selected.
SQL>
Description: cid:image003.png@01CD17D0.99AE3620
SQL>
col profile_option_value for A20;
col profile_option_id for 999999999;
select PROFILE_OPTION_ID, PROFILE_OPTION_VALUE from FND_PROFILE_OPTION_VALUES
where profile_option_id in (‘4176‘,’3098′,’3099’);
SQL>
Description: cid:image005.png@01CD17D0.99AE3620
SQL> update FND_PROFILE_OPTION_VALUES
set PROFILE_OPTION_VALUE = ‘Y’
where PROFILE_OPTION_VALUE = ‘N’
and PROFILE_OPTION_ID = 4176; 
Description: cid:image006.png@01CD17D0.99AE3620
2 rows updated.
SQL> commit;
Commit complete.
SQL>

col profile_option_value for A20;
col profile_option_id for 999999999;
select PROFILE_OPTION_ID, PROFILE_OPTION_VALUE from FND_PROFILE_OPTION_VALUES 
where profile_option_id in (‘4176′,’3098′,’3099’);  => All will show ‘Y’ now

Description: cid:image007.png@01CD17D0.99AE3620
To disable it, just set it to NO again:
SELECT PROFILE_OPTION_ID,PROFILE_OPTION_NAME FROM FND_PROFILE_OPTIONS_VL
WHERE START_DATE_ACTIVE <= SYSDATE
and NVL(END_DATE_ACTIVE,SYSDATE) >= SYSDATE
and ( SITE_ENABLED_FLAG = ‘Y’ or APP_ENABLED_FLAG = ‘Y’ or RESP_ENABLED_FLAG = ‘Y’ or USER_ENABLED_FLAG = ‘Y’ or SERVER_ENABLED_FLAG = ‘Y’ or SERVERRESP_ENABLED_FLAG = ‘Y’ or ORG_ENABLED_FLAG = ‘Y’)
and ( UPPER(USER_PROFILE_OPTION_NAME) LIKE ‘%FND%DEBUG%’
and (USER_PROFILE_OPTION_NAME LIKE ‘%f%’ or USER_PROFILE_OPTION_NAME LIKE ‘%F%’))
order by user_profile_option_name
PROFILE_OPTION_ID    PROFILE_OPTION_NAME
—————–    ——————-
4176                 AFLOG_ENABLED
3098                 AFLOG_FILENAME
3099                 AFLOG_LEVEL
8479                 AFLOG_BUFFER_MODE
3100                 AFLOG_MODULE
8465                 DEBUG RULE THRESHOLD
col profile_option_value for A20;
col profile_option_id for 999999999;
select PROFILE_OPTION_ID, PROFILE_OPTION_VALUE from FND_PROFILE_OPTION_VALUES
where profile_option_id in (‘4176‘,’3098′,’3099’);
PROFILE_OPTION_ID PROFILE_OP
—————– ———-
          3099       1
          4176       Y
          3098       NULL
SQL>

update FND_PROFILE_OPTION_VALUES
set PROFILE_OPTION_VALUE = ‘N’
where PROFILE_OPTION_VALUE = ‘Y’
and PROFILE_OPTION_ID = 4176;  => AFLOG_ENABLED will show ‘N’ now