What's wrong with my Audit Trail code?

[flower88]

I have this code to keep track of the changes in a form. It is suppose to tell me what was changed, when, and by whom. I have this code as a module

Public Function Audit_Trail()
On Error GoTo Err_Audit_Trail
    
    
    Dim MyForm As Form
    Dim ctl As Control
    Dim sUser As String
    Set MyForm = Screen.ActiveForm
    
    'If new record, record it in audit trail and exit function.
    If MyForm.NewRecord = True Then
        MyForm!AuditTrail = MyForm!tbAuditTrail & "New Record added on " & Now & " by " & UserName() & ";"
        Exit Function
    End If
    
    'Set date and current user if the form (current record) has been modified.
    MyForm!AuditTrail = MyForm!tbAuditTrail & vbCrLf & vbLf & "Changes made on " & Now & " by " & UserName() & ";"
    
    'Check each data entry control for change and record old value of the control.
    For Each ctl In MyForm.Controls
    
    'Only check data entry type controls.
    Select Case ctl.ControlType
    Case acTextBox, acComboBox, acListBox, acOptionGroup, acCheckBox
        If ctl.Name = "tbAuditTrail" Then GoTo TryNextControl 'Skip AuditTrail field.
            'If new and old value do not equal
            If ctl.Value <> ctl.OldValue Then
                MyForm!AuditTrail = MyForm!tbAuditTrail & vbCrLf & ctl.Name & ": Changed From: " & ctl.OldValue & ", To: " & ctl.Value
            'If old value is Null and new value is not Null
            ElseIf IsNull(ctl.OldValue) And Len(ctl.Value) > 0 Or ctl.OldValue = "" And Len(ctl.Value) > 0 Then
                MyForm!AuditTrail = MyForm!tbAuditTrail & vbCrLf & ctl.Name & ": Was Previoulsy Null, New Value: " & ctl.Value
            'If new value is Null and old value is not Null
            ElseIf IsNull(ctl.Value) And Len(ctl.OldValue) > 0 Or ctl.Value = "" And Len(ctl.OldValue) > 0 Then
                MyForm!AuditTrail = MyForm!tbAuditTrail & vbCrLf & ctl.Name & ": Changed From: " & ctl.OldValue & ", To: Null"
            End If
    End Select
    
TryNextControl:
    Next ctl
    
Exit_Audit_Trail:
    Exit Function
    
Err_Audit_Trail:
    If Err.Number = 64535 Then 'Operation is not supported for this type of object.
        Exit Function
    ElseIf Err.Number = 2475 Then 'You entered an expression that requires a form to be the active window
        Beep
        MsgBox "A form is required to be the active window!", vbCritical, "Invalid Active Window"
    Else
        Beep
        MsgBox Err.Number & " - " & Err.DESCRIPTION
    End If
    Resume Exit_Audit_Trail
    
End Function

and I'm calling the module in my form under before update like this:

On Error GoTo Form_BeforeUpdate_Err
    
    Call Audit_Trail
    
Form_BeforeUpdate_Exit:
    Exit Sub
    
Form_BeforeUpdate_Err:
    MsgBox Err.Number & " - " & Err.DESCRIPTION
    Resume Form_BeforeUpdate_Exit

Right now, it tells me when the record was added and by whom but if I go back and edit the record then it does nothing.

Any ideas?

Thanks for the help!