string myCommand = "SELECT * FROM Manager WHERE UserName=" + ID;

        SqlDataAdapter da = new SqlDataAdapter(myCommand, con);

        DataSet ds = new DataSet();

        try
        {
            con.Open();
            da.Fill(ds); // <- highlighting this part of the code..
        }
        finally
        {
            con.Close();
        }
        foreach (DataRow dr in ds.Tables[0].Rows)
        {
            txtUserName.Text = dr[1].ToString();

        }

    }
}

string myCommand = "SELECT * FROM Manager WHERE UserName='" + ID + "'";

private void simpleButton1_Click(object sender, EventArgs e)
{
	const string connStr = @"Data Source=apex2006sql;Initial Catalog=Leather;Integrated Security=True;";
	const string query = "Select * From Invoice Where InvNumber = @InvNumber";
	const int invNumber = 1100;
 
	DataSet ds = new DataSet();
 
	using (SqlConnection conn = new SqlConnection(connStr))
	{
		conn.Open();
		using (SqlCommand cmd = new SqlCommand(query, conn))
		{
			cmd.Parameters.Add("@InvNumber", SqlDbType.Int).Value = invNumber;
			using (SqlDataAdapter da = new SqlDataAdapter(cmd))
			{
				da.Fill(ds);
			}
		}
		conn.Close();
	}
}