i removed this part
con.Open();
string s = "SELECT user_name FROM login" + " WHERE user_name='" + Label1.Text + "'";
SqlCommand cmd = new SqlCommand(s, con);
SqlDataReader Dr = cmd.ExecuteReader();
if (Dr.Read())
{
con.Close();
}
and placed only this part in Load
private void LoadData()
{
DateTime datetime = Convert.ToDateTime(Date.Text);
SqlCommand cmnd = new SqlCommand("SELECT * FROM Tech_data where Call_assign= @Call_assign and dateadd(dd, datediff(dd,0, [date_time]), 0) = @date_time '");
cmnd.Connection = con;
cmnd.Parameters.Add("@Call_assing", SqlDbType.VarChar).Value = Label1.Text;
cmnd.Parameters.Add("@date_time", SqlDbType.DateTime).Value = datetime.Date;
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();
}