ACCESS VBA DATE IS BETWEEN

Hello experts, I've created a VBA function (below) that is giving me a complie error "sub or function is not defined". Could someone tell me where I might be going wrong or suggest a better way.

Background:
I want to update the PERIOD_ID field in the TBL_APPOINTMENT_DETAILS table to the value in ROW_ID in the TBL_REPORTING_PERIOD table.

TBL_APPOINTMENT_DETAILS:
EMP_NO   CHANGE_DATE        PERIOD_ROW_ID
33259VA  02/04/2008       *This should be 526            
33259VA  17/05/2008       *This should be 526                  
33259VA  09/06/2008       *This should be 526                  

TBL_REPORTING_PERIOD:
ROW_ID      TAX_YEAR QUARTER   PERIOD    DATE_FROM      DATE_TO
526      08/09       1               1                 01/04/2008      30/04/2008
527      08/09       1               2                 01/05/2008      31/05/2008
528      08/09       1               3                 01/06/2008      30/06/2008
-------------------------------
Function REPORTING_PERIOD(Change_Date As Date, DFrom As Date, DTo As Date, PERIOD_ID As Integer)
    If Change_Date Is between(DFrom And DTo) Then
        REPORTING_PERIOD = PERIOD
    Else
        REPORTING_PERIOD = 0
    End IfStart Free Trial