I have some problem with report filter

Dim st As String = frmCheckSale.StartDate.Value.ToString("MM/dd/yyyy")

    Dim rpt As New CSaleDetail
    rpt.RecordSelectionFormula = "{VSaleDetail.dates}>='" & st & "'"

VSaleHistory.RefreshReport()
    VSaleHistory.ReportSource = rpt

Dim st As String = frmCheckSale.StartDate.Value.ToString("MM/dd/yyyy")
    Dim ed As String = frmCheckSale.EndDate.Value.ToString("MM/dd/yyyy")

    Dim rpt As New CSaleDetail
    rpt.RecordSelectionFormula = "{VSaleDetail.dates}>='" & st & "' and {VSaleDetail.dates}=
    <'"& ed &"'"

VSaleHistory.RefreshReport()
    VSaleHistory.ReportSource = rpt