Crystal Reports Problem using Crystal Report .NET in ASP.NET

Message

   I developed an ASP.NET web page using as object Crystal Report. I'm
using multiview. After the report run, when I clicked Export or move to
the next page, the web page goes blank. I tried in different ways to
see the report. I have the following code:

 protected void Page_Load(object sender, EventArgs e)
    { // Begin Page_Load

        if (!Page.IsPostBack)
        { // Begin if
            mvwReport.SetActiveView(viewParameterPrompt);
        } // End if

    } // End Page_Load

To open the report I have the following code:

CrystalReportViewer1.ParameterFieldInfo = myPFs;
        CrystalReportViewer1.RefreshReport();
        mvwReport.SetActiveView(viewReportOnDemand);

I
don't understand why when I click any button of Crystal report the
report goes blank. I hope that someone can help me to handle this
issue. I appreciate any help or suggestion or idea.