I seem to have run into the same problems as RayA McCain but I've managed to solve the error messages & have a new problem.
The 2 issues that I found where:
1) there was no end if at the end of the nested elseif block
2) the video cut out the " & after the AND in the ReceivedPOs if statement. It should look like:
wherestr = wherestr & " AND " & wherestr = wherestr & "POReceived= true"

Now for my current problem:
When I select the openpos or receivedpos checkboxes the list box doesn't get filtered. Both it & the PODetail subform are blank. I've slightly altered the VBA code for my design purposes but the basis is the same.

Private Sub BuildPOList()

    Dim s As String
    Dim wherestr As String
    
    s = "SELECT PurchaseOrderID, VendorName, PODate FROM PurchaseOrderQ"
    wherestr = ""
    
    If OpenPOs = True Then
        wherestr = "IsOpen = True"
        OpenPOLabel.Caption = "Open PO's"
    ElseIf OpenPOs = False Then
        wherestr = "IsOpen = False"
        OpenPOLabel.Caption = "Closed PO's"
    End If
    
    If ReceivedPOs = True Then
        If wherestr <> "" Then
        wherestr = wherestr & " AND " & wherestr = wherestr & "POReceived= true"
        ReceivedPOLabel.Caption = "Received PO's"
        End If
    ElseIf ReceivedPOs = False Then
        If wherestr <> "" Then
        wherestr = wherestr & " AND " & wherestr = wherestr & "POReceived= false"
        ReceivedPOLabel.Caption = "Unreceived PO's"
        End If
    End If
    
    If wherestr <> "" Then
        s = s & " WHERE " & wherestr
    End If
    
        s = s & " ORDER BY PODate"
        
    POList.RowSource = s
    POList = POList.ItemData(0)
    PODetailUpdate
    
    If OpenPOs = True Then
        PurchaseOrderDetailF.Locked = False
    Else
        PurchaseOrderDetailF.Locked = True
    End If
    
End Sub

Any help would be much appreciated.
I'm loving these inventory management classes!
Thanks

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Reply from Alex Hedley:

I'd need to check into this as it's been a few years since I've watch this.

One thing to check might be
PODetailUpdate