not instance of an object (missing directive or assemble reference )

if (TextBox1.Text == "")
        {
            DataTable dt = new DataTable();
            SqlConnection con = new SqlConnection();
            con.ConnectionString = "Data Source=PALANIVEL;Initial Catalog=HMS;User ID=sa;Password=login";
            con.Open();
            SqlDataAdapter ad = new SqlDataAdapter();
         
            DateWiseIP t2 = new DateWiseIP();
 

            ad = new SqlDataAdapter("select * from  Vw_InPatient where Reg_Date between '"+TextBox1.Text+"' and '"+TextBox2.Text+"'", con);
            ad.Fill(dt);
            t2.SetDataSource(dt);
            CrystalReportViewer1.ReportSource = t2;
            CrystalReportViewer1.RefreshReport();
        }