Crystal report error message

i have applied CrystalReportSource in aspx page and in code tried this 

protected void Page_Load(object sender, EventArgs e)
        {
 ReportDocument crystalReport = new ReportDocument();
            crystalReport.Load(Server.MapPath("CrystalReport1.rpt"));
            crystalReport.SetDatabaseLogon("sa", "1234@@@89", @"Server", "database");
            CrystalReportViewer1.ReportSource = crystalReport;
}

It work fine .. it dont ask me login password...

but when i use parameter for search ID it is poping this message

Object reference not set to an instance of an object