"Data type mismatch in criteria expression." error in ms access, i did all the troubleshooting suggested - sql

Question

i get the error "Data type mismatch in criteria expression." in a query.
Like this the query works perfectly
WorkingDays([ORDER_NOTIFICATION_DATE],[OP_DISTRIBUTION_DATE]) AS
BOOKING_DAYS, IIf([BOOKING_DAYS]>8,"IS LATE","ON TIME") AS BOOKING_DELAYED
FROM JOB INNER JOIN [ORDER] ON JOB.[JOB_ID] = ORDER.[JOB_ID]
WHERE (((ORDER.ORDER_NOTIFICATION_DATE) Is Not Null) AND
((ORDER.OP_DISTRIBUTION_DATE) Is Not Null));
when i try to put another criteria it shows me the error:
WorkingDays([ORDER.ORDER_NOTIFICATION_DATE],[ORDER.OP_DISTRIBUTION_DATE]) AS
BOOKING_DAYS, IIf([BOOKING_DAYS]>8,"IS LATE","ON TIME") AS BOOKING_DELAYED
FROM JOB INNER JOIN [ORDER] ON JOB.[JOB_ID] = ORDER.[JOB_ID]
WHERE (((ORDER.ORDER_NOTIFICATION_DATE) Is Not Null) AND
((ORDER.OP_DISTRIBUTION_DATE) Is Not Null) AND
((WorkingDays([ORDER.ORDER_NOTIFICATION_DATE],
[ORDER.OP_DISTRIBUTION_DATE]))>8));
WorkingDays returns an integer, i tried most of the solutions proposed in other posts.
this is WorkingDays:
Public Function WorkingDays(StartDate As Date, EndDate As Date) As Integer
'....................................................................
' Name: WorkingDays
' Inputs: StartDate As Date
' EndDate As Date
' Returns: Integer
' Author: Arvin Meyer
' Date: February 19, 1997
' Comment: Accepts two dates and returns the number of weekdays between them
' Note that this function does not account for holidays.
'....................................................................
On Error GoTo Err_WorkingDays
Dim intCount As Integer
intCount = 0
Do While StartDate <= EndDate
'Make the above < and not <= to not count the EndDate
Select Case Weekday(StartDate)
Case Is = 1, 7
intCount = intCount
Case Is = 2, 3, 4, 5, 6
intCount = intCount + 1
End Select
StartDate = StartDate + 1
Loop
WorkingDays = intCount
Exit_WorkingDays:
Exit Function
Err_WorkingDays:
Select Case Err
Case Else
MsgBox Err.Description
Resume Exit_WorkingDays
End Select
End Function

Answer 1

I see you're using Is Not Null and a function that can't handle Null values in the same query.
While you may assume this could work just fine, as the Null values get filtered out, they still get passed to this function and create an error.
Use Nz to escape the nulls getting passed to the function:
WorkingDays(Nz([ORDER.ORDER_NOTIFICATION_DATE], 0),Nz([ORDER.OP_DISTRIBUTION_DATE], 0)) AS
BOOKING_DAYS, IIf([BOOKING_DAYS]>8,"IS LATE","ON TIME") AS BOOKING_DELAYED
FROM JOB INNER JOIN [ORDER] ON JOB.[JOB_ID] = ORDER.[JOB_ID]
WHERE (((ORDER.ORDER_NOTIFICATION_DATE) Is Not Null) AND
((ORDER.OP_DISTRIBUTION_DATE) Is Not Null) AND
((WorkingDays(Nz([ORDER.ORDER_NOTIFICATION_DATE], 0),
Nz([ORDER.OP_DISTRIBUTION_DATE], 0)))>8));