how to insert date in SQL server 2005 using C# .net?

Remove the spaces around the date:

SqlCommand cmd = new SqlCommand("insert into loginfo values('" + textBox1.Text + "',  '" + dateTimePicker1.Value.ToShortDateString()+ "' ", con);

Try this if it still has problems :

dateTimePicker1.Value.ToString("yyyy-MM-dd")

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["conm"].ConnectionString);
    SqlCommand cmd = new SqlCommand();
    SqlDataAdapter adp = new SqlDataAdapter();
    DataSet ds = new DataSet();

 try
        {


 cmd.Connection = conn;
            cmd.CommandType = CommandType.Text;
            // cmd.CommandText = "update ReglaCategorizacion set Ordenejecucion='" + lblOExecution.Text + "'where IdRegla='" + lblPreviousRegla.Text + "' ";
  cmd.CommandText = "insert into UserDetail(RoleID,FirstName,LastName)";
            cmd.Parameters.AddWithValue("@RoleID", Rdb_UserType.SelectedValue);
            cmd.Parameters.AddWithValue("@FirstName", txt_name.Text);
            cmd.Parameters.AddWithValue("@LastName", txt_Surname.Text);
           
            conn.Open();
            cmd.ExecuteNonQuery();
        }
        catch (Exception ex)
        {
            Response.Redirect("~/ErroPage.aspx?a=" + ex.Message);

        }

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;

namespace WindowsFormsApplication9
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
try
{
SqlConnection con = new SqlConnection("Data Source=AHSAN-PC\\SQLEXPRESS; Initial Catalog=waf; Integrated Security=SSPI;");
con.Open();
MessageBox.Show("Connection Established Successfully with Database", "Database Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
SqlCommand cmd = new SqlCommand("insert into loginfo values('" + textBox1.Text + "', ' " + dateTimePicker1.Value.ToShortDateString()+ " ' ", con);
cmd.ExecuteNonQuery();
MessageBox.Show("Insertion successfully done");
}
catch (Exception e1)
{
MessageBox.Show("error:" + e1.Message);
}

}
}
}

SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["conm"].ConnectionString);
    SqlCommand cmd = new SqlCommand();
    SqlDataAdapter adp = new SqlDataAdapter();
    DataSet ds = new DataSet();

 try
    {
 cmd.Connection = conn;
 cmd.CommandType = CommandType.Text;            
 cmd.CommandText = "insert into UserDetail(RoleID,FirstName,LastName)";
 cmd.Parameters.AddWithValue("@RoleID", Rdb_UserType.SelectedValue);
 cmd.Parameters.AddWithValue("@FirstName", txt_name.Text);
 cmd.Parameters.AddWithValue("@LastName", txt_Surname.Text);
           
  conn.Open();
  cmd.ExecuteNonQuery();
  }
  catch (Exception ex)
  {
  Response.Redirect("~/ErroPage.aspx?a=" + ex.Message);
  }