Dephi三层de迷惑

最近用D7写了一个三层数据库模型，使用了Remote Transactional Datamodule和TClientDataset组件，连接方式是SocketConnection。本来一开始运行的好好的，可是在服务器端程序改动一点点之后，便开始不正常，客户端访问的时候，抛出致命错误，也不知道致命在哪里。下面两段源代码经过比较，没发现有什么特别的改动。

{Code 1: 能够正常运行的代码}


unit uRead;
{$WARN SYMBOL_PLATFORM OFF}
interface
uses
    Windows,
    {.....}
    MidLayer_TLB,
    DB,
    ADODB,
    Provider;
type
    TReadFromDatabase = class(TMtsDataModule, IReadFromDatabase)
        conRead: TADOConnection;
        tblViewEmployees: TADOTable;
        cdsEmployees: TClientDataSet;
        dspEmployees: TDataSetProvider;
         {...}
    private
        { Private declarations }
    protected
        class procedure UpdateRegistry(Register: Boolean; const ClassID, ProgID:
            string); override;
        procedure PrepareEmployees; safecall;
        procedure Login; safecall;
        function SignIn(const ARef, APassword: WideString; ATimes: Integer;
            var AAdmin, ALogedSuccess, ARejected: WordBool): WideString;
            safecall;
    public
        { Public declarations }
    end;
var
    ReadFromDatabase: TReadFromDatabase;
implementation
uses
    IniFiles;
{$R *.DFM}
class procedure TReadFromDatabase.UpdateRegistry(Register: Boolean; const
    ClassID, ProgID: string);
begin
    if Register then
        begin
            inherited UpdateRegistry(Register, ClassID, ProgID);
            EnableSocketTransport(ClassID);
            EnableWebTransport(ClassID);
        end
    else
        begin
            DisableSocketTransport(ClassID);
            DisableWebTransport(ClassID);
            inherited UpdateRegistry(Register, ClassID, ProgID);
        end;
end;
procedure TReadFromDatabase.PrepareEmployees;
begin
    //reserved
end;
procedure TReadFromDatabase.Login;
begin
    //reserved
end;
function TReadFromDatabase.SignIn(const ARef, APassword: WideString;
    ATimes: Integer; var AAdmin, ALogedSuccess,
    ARejected: WordBool): WideString;
begin
    with TADOQuery.Create(nil) do
        try
            Connection := conRead;
            SQL.Add('SELECT Admin, FullName FROM Employees WHERE EmployeeRef=' +
                QuotedStr(ARef) + ' AND Password=' + QuotedStr(APassword));
            Open;
            if Eof then
                begin
                    Inc(ATimes);
                    ALogedSuccess := False;
                    if ATimes = 3 then
                        ARejected := True
                    else
                        ARejected := False;
                    AAdmin := False;
                    Result := '';
                end
            else
                begin
                    ALogedSuccess := True;
                    ARejected := False;
                    AAdmin := FieldByName('admin').AsBoolean;
                    Result := fieldbyname('FullName').AsString;
                end;
        finally
            Close;
            Free;
        end;
end;
initialization
    TComponentFactory.Create(ComServer, TReadFromDatabase,
        Class_ReadFromDatabase, ciMultiInstance, tmBoth);
end.


{Code 2: 运行不了的代码}
unit uRead;
{$WARN SYMBOL_PLATFORM OFF}
interface
uses
    {...}
    MidLayer_TLB,
    DB,
    ADODB,
    Provider;
type
    TReadFromDatabase = class(TMtsDataModule, IReadFromDatabase)
        tblViewEmployees: TADOTable;
        cdsEmployees: TClientDataSet;
        dspEmployees: TDataSetProvider;
        {...}
        conRead: TADOConnection;
        procedure MtsDataModuleCreate(Sender: TObject);
    private
        { Private declarations }
    protected
        class procedure UpdateRegistry(Register: Boolean; const ClassID, ProgID:
            string); override;
        procedure PrepareEmployees; safecall;
        procedure Login; safecall;
        function SignIn(const ARef, APassword: WideString; ATimes: Integer;
            var AAdmin, ALogedSuccess, ARejected: WordBool): WideString;
            safecall;
    public
        { Public declarations }
        constructor Create(AOwner: TComponent); override;
    end;
var
    ReadFromDatabase: TReadFromDatabase;
implementation
uses
    IniFiles,
    uLog;
{$R *.DFM}
class procedure TReadFromDatabase.UpdateRegistry(Register: Boolean; const
    ClassID, ProgID: string);
begin
    if Register then
        begin
            inherited UpdateRegistry(Register, ClassID, ProgID);
            EnableSocketTransport(ClassID);
            EnableWebTransport(ClassID);
        end
    else
        begin
            DisableSocketTransport(ClassID);
            DisableWebTransport(ClassID);
            inherited UpdateRegistry(Register, ClassID, ProgID);
        end;
end;
procedure TReadFromDatabase.PrepareEmployees;
begin
    //reserved
end;
procedure TReadFromDatabase.Login;
begin
    //reserved
end;
function TReadFromDatabase.SignIn(const ARef, APassword: WideString;
    ATimes: Integer; var AAdmin, ALogedSuccess,
    ARejected: WordBool): WideString;
begin
    with TADOQuery.Create(nil) do
        try
            if not conRead.Connected then
              conRead.Open();
            Connection := conRead;
            SQL.Add('SELECT Admin, FullName FROM Employees WHERE EmployeeRef=' +
                QuotedStr(ARef) + ' AND Password=' + QuotedStr(APassword));
            Open;
            if Eof then
                begin
                    Inc(ATimes);
                    ALogedSuccess := False;
                    if ATimes = 3 then
                        ARejected := True
                    else
                        ARejected := False;
                    AAdmin := False;
                    Result := '';
                end
            else
                begin
                    ALogedSuccess := True;
                    ARejected := False;
                    AAdmin := FieldByName('admin').AsBoolean;
                    Result := fieldbyname('FullName').AsString;
                end;
        finally
            Close;
            Free;
        end;
end;
constructor TReadFromDatabase.Create(AOwner: TComponent);
begin
end;
procedure TReadFromDatabase.MtsDataModuleCreate(Sender: TObject);
var
    Loger           : TLoger;
    msg             : WideString;
begin
//    if conRead.Connected then
//        msg := FormatDateTime('mm-dd hh:nn:ss', Now) + ':  Opened on ' +
//            conRead.ConnectionString
//    else
//        msg := FormatDateTime('mm-dd hh:nn:ss', Now) + ': is closed ';
//    Loger.Log(msg);
//    ShowMessage(msg);
end;
initialization
    TComponentFactory.Create(ComServer, TReadFromDatabase,
        Class_ReadFromDatabase, ciMultiInstance, tmBoth);
end.


先记录下来，过段时间再回头研究到底是什么问题。