MS Access update statement with subquery in the set clause?

Experts,
I am trying to run the following update this update statement works:

UPDATE MJM_ATTEND_PAY_INDIV SET MJM_ATTEND_PAY_INDIV.ATTEND_PER_MONTH = 4
WHERE (((MJM_ATTEND_PAY_INDIV.ROW_ID) In (SELECT [MJM_ATTEND_PAY_INDIV].[ROW_ID]
FROM MJM_SCHOOL, MJM_CLASS, MJM_STUDENT, MJM_ATTEND_PAY_INDIV
WHERE [MJM_SCHOOL].[ROW_ID]=[MJM_CLASS].[SCHOOL_ID] And
[MJM_CLASS].[ROW_ID]=[MJM_STUDENT].[CLASS_ID] And
[MJM_STUDENT].[ROW_ID]=[MJM_ATTEND_PAY_INDIV].[STUDENT_ID] And
[MJM_STUDENT].[ACTIVE_FLG] = -1 And  
[MJM_ATTEND_PAY_INDIV].[PAID_FLG]=0 And
[MJM_SCHOOL].[ROW_ID] IN (select row_id  from mjm_school as sc where sc.active_flg = -1 and sc.billing_flg = -1 and sc.payment_type = 'Individual') And
[MJM_ATTEND_PAY_INDIV].[BILLING_MONTH]=[Date])));

However instead of hardcoding the number 4 at the end of the set statement, I want to use a subselect:

UPDATE MJM_ATTEND_PAY_INDIV SET MJM_ATTEND_PAY_INDIV.ATTEND_PER_MONTH = (select config_value from mjm_lu_config where config_type = 'Week Override')
WHERE (((MJM_ATTEND_PAY_INDIV.ROW_ID) In (SELECT [MJM_ATTEND_PAY_INDIV].[ROW_ID]
FROM MJM_SCHOOL, MJM_CLASS, MJM_STUDENT, MJM_ATTEND_PAY_INDIV
WHERE [MJM_SCHOOL].[ROW_ID]=[MJM_CLASS].[SCHOOL_ID] And
[MJM_CLASS].[ROW_ID]=[MJM_STUDENT].[CLASS_ID] And
[MJM_STUDENT].[ROW_ID]=[MJM_ATTEND_PAY_INDIV].[STUDENT_ID] And
[MJM_STUDENT].[ACTIVE_FLG] = -1 And  
[MJM_ATTEND_PAY_INDIV].[PAID_FLG]=0 And
[MJM_SCHOOL].[ROW_ID] IN (select row_id  from mjm_school as sc where sc.active_flg = -1 and sc.billing_flg = -1 and sc.payment_type = 'Individual') And
[MJM_ATTEND_PAY_INDIV].[BILLING_MONTH]=[Date])));

I know the subselect only returns 1 row.  However, when I do this I get an error that says "query must be updateable".

I would think I would be able to do this, am I doing something wrong?

Thank you in advance for the help.

- Mike