Sub CorrelationReproCode()
Dim conn As ADODB.Connection
Dim cmd As ADODB.Command
Dim sql As String
Dim fUseOutOfOrderUNION As Boolean

    Set conn = New ADODB.Connection
    conn.Open "Provider=sqloledb;Server=.;Database=northwind;" & _
              "Integrated Security=SSPI;"
    
    ' Change this to False to avoid the problem.
    fUseOutOfOrderUNION = True
    
    If (fUseOutOfOrderUNION) Then
        sql = "SELECT O.OrderDate FROM Customers R, Orders O " & _
              "WHERE R.CustomerId = O.CustomerId AND R.CustomerId = ? " & _
              "Union " & _
              "SELECT O.OrderDate FROM Orders O, Customers R " & _
              "WHERE R.CustomerID = O.CustomerID AND R.Region = ?"
    Else
        sql = "SELECT O.OrderDate FROM Customers R, Orders O " & _
              "WHERE R.CustomerId = O.CustomerId AND R.CustomerId = ? " & _
              "Union " & _
              "SELECT O.OrderDate FROM Customers R, Orders O " & _
              "WHERE R.CustomerID = O.CustomerID AND R.Region = ?"
    End If
    Set cmd = New ADODB.Command
    cmd.CommandText = sql
    Set cmd.ActiveConnection = conn

    ' Error will occur here if fUseOutOfOrderUNION is set to True.
    cmd.Parameters.Refresh
    Set cmd.ActiveConnection = Nothing
    Set cmd = Nothing
    conn.Close
    Set conn = Nothing
    
End Sub