以下是IdTCPServerConnect事件登录部分的代码。
当客户端达到大约20时，新的客户端试图登录时，新的客户端显示“connection closed gracefully”,
但服务器仍然可以对已登录的客户进行服务，但服务器这时不能正常关闭，试图关闭服务器，显示：
“Accessviolation at address 00408904 in module ‘Server.exe’.Read of address 00000000.

procedure TFormServer.IdTCPServerConnect (AContext: TIdContext);”
var
  Client:              TUser;
  AUserName, Password: string;
  FirstReceiveString:  string;
  lst:                 TList;
  i:                   integer;
   
function ReadUserName(LoginName:string):Boolean;
var
  ADOQuery: TADOQuery;
  MyString: string;
begin
  Lock;
  try
    CoInitialize(nil);
    ADOQuery := TADOQuery.Create(nil);
    ForceConnectedToDatabase(true);
    try
      try
        Result:=false;
        ADOQuery.Connection := ADOConnection;
        ADOQuery.Close;
        ADOQuery.SQL.Clear;
        ADOQuery.SQL.Add('SELECT * From UserInfomation');
        ADOQuery.Open;
        while not ADOQuery.Eof do
        begin
          MyString:=ADOQuery.FieldByName('UserName').AsString;

          if MyString=LoginName then Result:=true;
          ADOQuery.Next;
        end;
      finally
        ADOQuery.Free;
        CoUnInitialize;
      end;
    except
      Result := False;
    end;
  finally
    Unlock;
  end;
end;

function ReadUserPassW(PassW:string):Boolean;
var
  ADOQuery: TADOQuery;
  MyString:  string;
begin
  Lock;
  try
    CoInitialize(nil);
    ADOQuery := TADOQuery.Create(nil);
    ForceConnectedToDatabase(true);
    try
      try
        Result:=false;
        ADOQuery.Connection := ADOConnection;
        ADOQuery.Close;
        ADOQuery.SQL.Clear;
        ADOQuery.SQL.Add('SELECT * From UserInfomation');
        ADOQuery.Open;
        while not ADOQuery.Eof do
        begin
          MyString:=ADOQuery.FieldByName('Pass').AsString;
          if  (MyString=PassW) then Result:=true;
          ADOQuery.Next;
        end;
      finally
        ADOQuery.Free;
        CoUnInitialize;
      end;
    except
      Result := False;
    end;
  finally
    Unlock;
  end;
end;

begin
  FirstReceiveString := AContext.Connection.IOHandler.ReadLn;

    if FirstReceiveString = '' then
    begin
      AContext.Connection.IOHandler.WriteLn('NO_USER_NAME');
      AContext.Connection.Disconnect;
      Exit;
    end;
    i := pos(' ', FirstReceiveString);
    AUserName := Copy(FirstReceiveString, 1, i - 1);
    Delete(FirstReceiveString, 1, i);
    Password := FirstReceiveString;
    lst := FUsers.LockList;

    try
      FLockUI.Enter;
      try
        if ReadUserName(AUserName)=false then
        begin
          AContext.Connection.IOHandler.WriteLn('NotRegistered');
          exit;
        end;

        if ReadUserPassW(Password)=false then
        begin
          AContext.Connection.IOHandler.WriteLn('WrongPassword');
          exit;
        end;
      finally
        FLockUI.Leave;
      end;

      for i := 0 to lst.Count - 1 do
      begin
        if SameText(TUser(lst[I]).UserName, AUserName) then
        begin
          AContext.Connection.IOHandler.WriteLn('USER_ALREADY_LOGINED');
          AContext.Connection.Disconnect;
          Exit;
        end;
      end;
      Client := TUser.Create(AContext.Binding.PeerIP, AUserName,
        AContext.Binding.PeerPort, AContext);
      lst.Add(Client);
      CCount := CCount + 1;
      CData.PlayerName[lst.Count - 1] := AUserName;

      Client.Lock;
      try
        Client.Context.Connection.IOHandler.WriteLn('LOGINED' + ' ' + IntToStr(lvUsers.Items.Count));

      finally
        Client.Unlock;
      end;
    finally
      FUsers.UnlockList;
    end;
    SendMessage(FormHanlde, WM_REFRESH_USERS, Ord(rpAppendItem), integer(Client));

  End;