reporting-services - the source of the report definition is not specified

Question

Public Sub StudentList(ByVal CourseID As String, ByVal SY As String)
    RptVwer.Reset()
    RptVwer.ProcessingMode = Microsoft.Reporting.WinForms.ProcessingMode.Local
    RptVwer.LocalReport.ReportPath = Environment.CurrentDirectory + "\StudentList.rdl"

    Dim paramList As New Generic.List(Of ReportParameter)

    paramList.Add(New ReportParameter("fxKeyCourseID", CourseID, False))
    paramList.Add(New ReportParameter("fxKeySchoolYear", SY, False))
    RptVwer.LocalReport.SetParameters(paramList)   

    Dim dsSummary As DataSet = modReport.StudentList_sp(CourseID, SY)
    Dim rDs As ReportDataSource = New ReportDataSource("DataSet1", dsSummary.Tables(0))
    RptVwer.LocalReport.DataSources.Clear()
    RptVwer.LocalReport.DataSources.Add(rDs)
    RptVwer.ServerReport.Refresh()
    RptVwer.RefreshReport()

End Sub

i'm using SSRS report in vb.net 2010 (sql server database). the report viewer is viewing but display an error "the source of the report definition is not specified". Please help me.above is my exact code.