You need to add the login credentials of Database as below
protected void Page_Load(object sender, EventArgs e)
{
ReportDocument crystalReport = new ReportDocument();
crystalReport.Load(Server.MapPath("CrystalReport.rpt"));
crystalReport.SetDatabaseLogon
("amit", "password", @"AMIT\SQLEXPRESS", "TestDB");
CrystalReportViewer1.ReportSource = crystalReport;
}