Program crashes when I try to export to pdf file using CR for VS2010

Question

I'm using VS2010, framework 4.0. I can view, print, and export the report to excel. When I click export, select pdf, enter a file name, and click save...I get the following message:
Value cannot be null.
Parameter name: window
I added Ludek's code to limit exports to pdf and excel to my JPTreportView.xaml.vb file:
Public Class JPTReportView
        Private Sub UserControl_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
            reportViewer.ViewerCore.ReportSource = Me.DataContext.ReportSource
            reportViewer.ViewerCore.ToggleGroupTree = False
            reportViewer.ViewerCore.ToggleParameterPanel = False
            reportViewer.ViewerCore.ToggleSidePanel = False
            Dim exportFlags = (CrystalDecisions.Shared.ViewerExportFormats.PdfFormat Or CrystalDecisions.Shared.ViewerExportFormats.ExcelFormat)
            reportViewer.ViewerCore.AllowedExportFormats = exportFlags
        End Sub
    End Class

Answer 1

My parameters are set in the code and are set to "Do not show" in the report. The pdf export did not work before I added the code to limit the export options. The code in JptReportView.xaml:
<UserControl xmlns:my="clr-namespace:SAPBusinessObjects.WPF.Viewer;assembly=SAPBusinessObjects.WPF.Viewer"
             x:Class="View.JPTReportView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <my:CrystalReportsViewer Name="reportViewer" ShowOpenFileButton="False" ShowToggleSidePanelButton="False"     ShowRefreshButton="False" ShowLogo="False" Focusable="True" />
</UserControl>