Parameters in Crystal Reports 9 through VS.Net 2003

I am trying to set parameters correctly in an ASP.Net page for a crystal report but keep getting the message: Missing parameter field current value. Here is my current code:

CRV1.ReportSource = myReport
Dim ParameterFields As ParameterFields
ParameterFields = CRV1.ParameterFieldInfo
If Session.Item("Parm") <> "" Then
    Dim strParmName As String, strParmVal As String
    strParmName = Session.Item("ParmName")
    strParmVal = Session.Item("Parm")
    myReport.SetParameterValue(0, strParmVal)
Else
    Dim ParameterField As ParameterField
    ParameterField = ParameterFields.Item(0)
    If myReport.DataDefinition.ParameterFields(0).DefaultValues.Count > 0 Then
        ParameterField.CurrentValues = ParameterField.DefaultValues
    Else
        ParameterField.EnableNullValue = True
    End If
End If

Neither the Default nor the EnableNullValue seem to work.  What am I doing wrong - I can't seem to find any documentation on this for crystal 9.