I fixed the problems and now everything works to pass start and end date parameters to my Crystal Report in VB.NET...

Here is the wild and crazy code that actually works to pass parameters to a Crystal Report from VB.NET app (front-end menu to Crystal Reports) so users can choose a report from a menu and run it. If the report has start and end date parameters, this code plugs them into the report and preview the report in a form's window that contains a Crystal Reports Viewer object...

    Dim crxApplication As New CRAXDRT.Application
    Public oReport As CRAXDRT.Report
    Public cboRpt1, cboRpt2 As String
    Public start_date, end_date As String

    Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        If cboRpt1 = 0 And cboRpt2 = 0 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
            oReport.ParameterFields.Item(1).AddCurrentValue(CDate(F1.TextBox2.Text))
            oReport.ParameterFields.Item(2).AddCurrentValue(CDate(F1.TextBox3.Text))
        ElseIf cboRpt1 = 0 And cboRpt2 = 1 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
            oReport.ParameterFields.Item(1).AddCurrentValue(CDate(F1.TextBox2.Text))
            oReport.ParameterFields.Item(2).AddCurrentValue(CDate(F1.TextBox3.Text))
        ElseIf cboRpt1 = 0 And cboRpt2 = 2 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
            oReport.ParameterFields.Item(1).AddCurrentValue(CDate(F1.TextBox2.Text))
            oReport.ParameterFields.Item(2).AddCurrentValue(CDate(F1.TextBox3.Text))
        ElseIf cboRpt1 = 1 And cboRpt2 = 0 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 1 And cboRpt2 = 1 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 1 And cboRpt2 = 2 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 1 And cboRpt2 = 3 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
            oReport.ParameterFields.Item(1).AddCurrentValue(CDate(F1.TextBox2.Text))
            oReport.ParameterFields.Item(2).AddCurrentValue(CDate(F1.TextBox3.Text))
        ElseIf cboRpt1 = 1 And cboRpt2 = 4 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
            oReport.ParameterFields.Item(1).AddCurrentValue(CDate(F1.TextBox2.Text))
            oReport.ParameterFields.Item(2).AddCurrentValue(CDate(F1.TextBox3.Text))
        ElseIf cboRpt1 = 2 And cboRpt2 = 0 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 2 And cboRpt2 = 1 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 2 And cboRpt2 = 2 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 2 And cboRpt2 = 3 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 2 And cboRpt2 = 4 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        ElseIf cboRpt1 = 2 And cboRpt2 = 5 Then
            oReport = crxApplication.OpenReport("c:\crystal_test.rpt", 1)
        End If

        crViewer.ReportSource = oReport
        crViewer.ViewReport()
    End Sub