Asp.net Crystal 10 passing parameters

Hi,
I am using a webform with one text box to pass a string parameter to a CR. The code is below.
When the page loads it asks..
The report you requested requires further information.

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and has a textbox for the param. If I ignore this and enter my param the CR opens and displays correctly. I thought setting
CrystalReportViewer1.EnableParameterPrompt = False  in   the page load would stop this, but I get an error
Missing parameter values.

Anyone have any suggestions?

 Private Sub GenerateRPT(ByVal ProductID As String)
        ' Declare variables needed to pass the parameters
        ' to the viewer control.
        Dim paramFields As New ParameterFields()
        Dim paramField As New ParameterField()
        Dim discreteVal As New ParameterDiscreteValue()
        'Dim rangeVal As New ParameterRangeValue()

        ' The first parameter is a discrete parameter with multiple values.

        ' Set the name of the parameter field, this must match a
        ' parameter in the report.
        paramField.ParameterFieldName = "ProductID"

        ' Set the first discrete value and pass it to the parameter
        discreteVal.Value = ProductID
        paramField.CurrentValues.Add(discreteVal)

 
        paramFields.Add(paramField)

        ' Set the parameter fields collection into the viewer control.
        CrystalReportViewer1.ParameterFieldInfo = paramFields
        CrystalReportViewer1.ReportSource = New Report1()


    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim ProdId As String
        ProdId = txtProductID.Text
        GenerateRPT(ProdId)
    End Sub