CrystalReport is not visible in asp.net c#

I am making a simple crystal report on asp.net c#. When I run it in browser, the report isn't visible. Although there are no errors. What am I missing?

Here is my code behind on Load Event to load crystal Report in CrystalReportViewer.

    SqlConnection con;
    string connString = null;
    connString = "Data Source=.;initial catalog=InvoiceSystem;user id=sa;password=rfm";
    con = new SqlConnection(connString);
    con.Open();

    string query = null;
    query = "Select * from tblInvoice";
    SqlDataAdapter da = new SqlDataAdapter(query, con);
    con.Close();
    DataSetInv ds = new DataSetInv();
    da.Fill(ds, "tblInvoice");
    ReportDocument rpt = new ReportDocument();
    rpt.Load(Server.MapPath("~/CrystalReportInv.rpt"));
    rpt.SetDataSource(ds);
    CrystalReportViewer1.ReportSource = rpt;