when i run the report Load Report Failed Error Occurs what is the problem

Question

 con = new SqlConnection("Server=(local);initial catalog=ServiceTax;Trusted_Connection=True");

            con.Open();

            string str = "select * from diesel where Billno='" + cb_billno.SelectedItem + "'";

            SqlCommand com = new SqlCommand(str, con);

            SqlDataAdapter sqlda = new SqlDataAdapter(com);

            DataSet ds = new DataSet();

            sqlda.Fill(ds, "diesel");

            con.Close();

            ReportDocument r1 = new ReportDocument();

            r1.Load("Reports/Service Bill.rpt");

            r1.SetDataSource(ds);

            crystalReportViewer1.ReportSource = r1;

            crystalReportViewer1.RefreshReport();

In the run mode i have  one textbox and one button.in that textbox i type the partucular Bill no and click the button Error Shows as Load Report Failed.

Erro Shows in    r1.Load("Reports/Service Bill.rpt"); (Load reprot Failed)

Billno  Datatype in Varchar.

For Example R004 and click the button the partiuclar Bill datas want to be appear in crystal report Viewer in Run Mode.