Login code error in 3-Tier

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C#3.5

I am getting error on my code given below(VS 2010). Error is "{"Object reference not set to an instance of an object."}. However the same code runs fine in VS 2008. Please help me. Thanks in advance.

////DAL
 public DataTable LoadUserName()
    {
        DataTable dTable = null;

        try
        {
            con.Open();

            String selectStr = "select uCode,uID,uPassword from tUsers";
            SqlDataAdapter da = new SqlDataAdapter(selectStr, con);
            
            dTable = new DataTable();

            da.Fill(dTable);

            con.Close();   

        }
        catch (Exception e)
        {
            String Str = e.Message;
        }

        return dTable;
    }

///BAL


public bool authenticate(string username, string password)
    {
        LoginDAL dal = new LoginDAL();
        DataTable dTable = dal.LoadUserName();

        bool found = false;
        
        foreach (DataRow dRow in dTable.Rows)                 ///Getting error on this line
        {
            if ((username == dRow["uID"].ToString()) &&
                         password == dRow["uPassword"].ToString())
            {
                userID =Convert.ToInt32(dRow["uCode"].ToString());
                found = true;
            }
        }
        if
            (!found)
        {
            return false;
        }

        return found;

    }