I'm not sure why this is not working.  It is returning all records instead
of just the desired criteria:

Report Source is:
 SELECT InvoiceHeader.*, InvoiceDetail.*, Trim(InvoiceHeader!fname) & " " &
Trim(InvoiceHeader!lname) AS Printname FROM InvoiceHeader INNER JOIN
InvoiceDetail ON InvoiceHeader.Recno=InvoiceDetail.InvoiceRecno;

Here is the code from my form's button:
Private Sub btnPrintNow_Click()
Dim stReportname As String
Dim stCriteria As String

stReportname = "rptInvoice"

With Me!Recno
       If Not IsNull(.Value) Then
              strCriteria = "[InvoiceHeader.Recno] = " & .Value
       End If
   End With

MsgBox strCriteria
DoCmd.OpenReport stReportname, acViewPreview, Wherecondition:=stCriteria
End Sub

The msgbox is showing the criteria to be correct, but all the records are
still being selected.