retrieving a datetime value from sql using the select statement

i wanted to get the Sign_in and Date columns from the database using the select query but when i run the following code i get an error at the while(dr.Read()).......n the error is "Conversion failed when converting date and/or time from character string."the error is occuring from the while loop onwards......please sumone could tell me where im making a mistake?? 

following is my code:

 private void button1_Click(object sender, EventArgs e)
        {
           
            login lg = new login();
            String b = lg.getData();
            //DateTime dt = dateTimePicker1.Value;
            conn = new SqlConnection(@"Data Source=RAMESH\SQLEXPRESS;Initial Catalog=Payroll;Integrated Security=True");
            conn.Open();
           
            string str = "select Sign_in,Date from Attendance where Eno='" +b+ "'and Date='"+dateTimePicker1.Value.Date+"'";
            cmd = new SqlCommand(str, conn);
            dr = cmd.ExecuteReader();
            

            while (dr.Read())
            {
                MessageBox.Show(dateTimePicker1.Text);
                String signin = dr[2].ToString();
                DateTime dat = DateTimedr[1];

               if ( dat==dateTimePicker1.Value && signin != " ")
                {
                    MessageBox.Show("u have signed in already");
                    signin_textBox.Clear();
                }
                else if(dat.ToString()==" " && signin=="")
                {
                    string time = DateTime.Now.ToString("hh:mm:ss tt");
                    signin_textBox.Text = time;
                }
            }
            dr.Close();
            conn.Close();
        }