C# ta sql e kayıt eklemede hata alıyorum yardım edermisiniz ?

using System; 
  using System.Collections.Generic; 
  using System.ComponentModel; 
  using System.Data; 
  using System.Drawing; 
  using System.Linq; 
  using System.Text; 
  using System.Windows.Forms; 
  using System.Data.SqlClient; 
  using System.Data.OleDb; 
   
  namespace Randevu 
  { 
      public partial class Form1 : Form 
      { 
          public Form1() 
          { 
              InitializeComponent(); 
          } 
   
          private void polikliniklerBindingNavigatorSaveItem_Click(object sender, EventArgs e) 
          { 
              this.Validate(); 
              this.polikliniklerBindingSource.EndEdit(); 
              this.tableAdapterManager.UpdateAll(this.erenn); 
   
          } 
   
          private void Form1_Load(object sender, EventArgs e) 
          { 
              // TODO: This line of code loads data into the 'erenn.Doktorlar' table. You can move, or remove it, as needed. 
              this.doktorlarTableAdapter.Fill(this.erenn.Doktorlar); 
              // TODO: This line of code loads data into the 'erenn.Hasta_Kayit' table. You can move, or remove it, as needed. 
              this.hasta_KayitTableAdapter.Fill(this.erenn.Hasta_Kayit); 
              // TODO: This line of code loads data into the 'erenn.Poliklinikler' table. You can move, or remove it, as needed. 
              this.polikliniklerTableAdapter.Fill(this.erenn.Poliklinikler); 
   
          } 
   
          private void comboBox1_SelectedIndexChanged(object sender, EventArgs e) 
          { 
              int a = Convert.ToInt32(comboBox1.SelectedIndex.ToString()) + 1; 
              SqlConnection sqlConn = new SqlConnection(@"data source=(local); initial catalog=erenn; integrated security=true"); 
              sqlConn.Open(); 
   
              SqlCommand sqlComCustomers = new SqlCommand(); 
              sqlComCustomers.CommandText = "select * from Doktorlar where Doktor_Numara='" + Convert.ToString(a) + "'"; 
              sqlComCustomers.CommandType = CommandType.Text; 
              sqlComCustomers.Connection = sqlConn; 
   
              SqlDataAdapter da = new SqlDataAdapter(); 
              da.SelectCommand = sqlComCustomers; 
   
              DataTable dtCustomers = new DataTable(); 
              da.Fill(dtCustomers); 
              comboBox2.DataSource = dtCustomers; 
          } 
   
          private void fillByToolStripButton_Click(object sender, EventArgs e) 
          { 
              try 
              { 
                  this.polikliniklerTableAdapter.FillBy(this.erenn.Poliklinikler); 
              } 
              catch (System.Exception ex) 
              { 
                  System.Windows.Forms.MessageBox.Show(ex.Message); 
              } 
   
          } 
   
          private void button1_Click(object sender, EventArgs e) 
          { 
              SqlConnection baglanti = new SqlConnection(@"data Source=EREN\\Eren; database =erenn; initial catalog=vt1; integrated security=true"); 
   
              baglanti.Open(); 
   
              DataSet ds = new DataSet(); 
              SqlCommand com = new SqlCommand("select * from Hasta_Kayit", baglanti); 
   
              SqlDataAdapter da = new SqlDataAdapter(com); 
              da.Fill(ds, "Hasta_Kayit"); 
              DataRow kayit; 
   
              kayit = ds.Tables["Hasta_Kayit"].NewRow(); 
   
              kayit["hasta_tc_no"] = hasta_tc_noTextBox.Text; 
              kayit["hasta_adi"] = hasta_adiTextBox.Text; 
              kayit["hasta_soyadi"] = hasta_soyadiTextBox.Text; 
   
              ds.Tables["Hasta_Kayit"].Rows.Add(kayit); 
   
              SqlCommandBuilder cmb = new SqlCommandBuilder(da); 
              da.Update(ds.Tables["Hasta_Kayit"]); 
              baglanti.Close(); 
          } 
   
          private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e) 
          { 
   
          } 
          } 
      }