I'm having some problem refreshing my viewer.

What happens is Im having error when i use .RefreshReport(). If I will not use the method, the report will run but will display old report. Please help me. Here's my code snippet:

.......
        report.FileName = appPath + reportType
        crReportDocument.Load(appPath + reportType)
        CrystalReportSource1.Report = report
        crReportDocument.SetDatabaseLogon("login", "admin", "SRV", "myDB")
        param.Name = "PayPeriod"
        paramValue.Value = Session("sessionReportValue").ToString()
        param.CurrentValues.Add(paramValue)
        CrystalReportViewer.ReportSource = CrystalReportSource1
        CrystalReportViewer.RefreshReport()
.....