OleDbCommand aCommand = new OleDbCommand("insert into customer_info(lr_no,date,customer_name,place,item_name,item_size,item_quantity,item_rate,total_rate,no_of_goods_fowarded) " + " values('" + textBox2.Text + "','" + dateTimePicker1.Value + "','" + comboBox1.Text + "','" + textBox1.Text + "','" + comboBox2.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + textBox6.Text + "','" + textBox3.Text + "','" + textBox7.Text + "') ");

Use parameterized queries. You will actually be able to read the SQL, prevent SQL injection, and have better performance on the sql server.

Here is an example for Sql* but you can change the typename to OleDb and use it the same way:

private void simpleButton1_Click(object sender, EventArgs e)
    {
      const string query = "Insert Into Employees (RepNumber, HireDate) Values (@RepNumber, @HireDate)";

      string connStr = BuildSqlNativeConnStr("apex2006sql", "Leather");
      DataTable dt;
      using (SqlConnection conn = new SqlConnection(connStr))
      {
        conn.Open();
        using (SqlCommand cmd = new SqlCommand(query, conn))
        {
          cmd.Parameters.Add(new SqlParameter("@RepNumber", 50));
          cmd.Parameters.Add(new SqlParameter("@HireDate", DateTime.Today));
          SqlDataReader dr = cmd.ExecuteReader();
          dt = new DataTable();
          dt.Load(dr);
        }
      }
      System.Diagnostics.Debugger.Break(); //At this point you have the populated datatable
    }

Also -- do this to your code and paste the result:

private void simpleButton2_Click(object sender, EventArgs e)
    {
      OleDbCommand cmd = new OleDbCommand("some " + "real " + "long " + " query");
      string cmdText = cmd.CommandText;
      System.Diagnostics.Debugger.Break();
    }

Paste the value of cmdText so we can see what is wrong with the query. It could be an issue with the values of one of your form components.