内存泄露问题！

定义了一个通信动态库文件，定义4个接口供主台调用，主台现在做一个监控程序需要循环抄读数据，且不停的调用这个动态库接口InitComm，Sendframe，Closecomm，需要不停的创建和释放串口，在这个动态库中使用的是Delphi的第三方控件Spcomm，问题的是有时候循环几十次出问题，有时候循环几百次出问题，都报的是内存泄露那里的错，估计是哪里内存没释放掉，报错地方都是CloseComm接口中调用FreeAndnil这个函数，请高手赐教！
unit PC_P_Comm;interfaceUses
  SpComm,Windows,Forms,SysUtils,Classes,Dialogs,ScktComp,XMLDoc,XMLIntf,
  IdBaseComponent, IdComponent;
type
   TBaseComm=Class(TObject)                        //The Base Comm;
   private
     procedure AnalyseCommParamXML(Str_XML:string);
     function  Check1107RecFrameEnd(Str_RecFrame:string):Integer;
     function  Check62056RecFrameEnd(Str_RecFrame:string):Integer;
     procedure Delay(i_Msc:LongInt);
     function  GetErrorMsg(i_ErrorCode:Integer):string;
   public
     constructor Create();overload;
     destructor  Destroy();override;
     function    InitComm(Str_XML:string):Integer;virtual;abstract;
     function    SendFrame(Str_SendFrame:string;var Str_RecFrame:string):Integer;virtual;abstract;
     function    StopComm():Integer;virtual;abstract;
   end;   TLocalComm=Class(TBaseComm)                     //The Class of Port Comm;
   private
     Comm:TComm;
     procedure CommReceiveData(Sender: TObject; Buffer: Pointer;BufferLength: Word);
   public
     constructor Create();overload;
     destructor  Destroy();override;
     function    InitComm(Str_XML:string):Integer;override;
     function    SendFrame(Str_SendFrame:string;var Str_RecFrame:string):Integer;override;
     function    StopComm():Integer;override;
   end;
var
  Gl_Str_CommTypeNo:string;
  Gl_Cls_LocalComm:TLocalComm;
  //供主台调用的四个接口 
  function InitComm(P_Str_XML,P_Str_Error:PChar):Integer;stdcall;
  function SendFrame(P_Str_SendFrame,P_Str_RecFrame,P_Str_Error:PChar;i_NewBaudrate:Integer=0):Integer;stdcall;
  function StopComm():Integer;stdcall;
  function CloseComm():Integer;stdcall;implementation//Initial the Communication(External Interface)
function InitComm(P_Str_XML,P_Str_Error:PChar):Integer;stdcall;
var
    Str_CommTypeNo:string;
begin
    //创建对象
    Gl_Cls_LocalComm:=TLocalComm.Create;
    Result:=Gl_Cls_LocalComm.InitComm(Str_InXML);
    if Result<0 then
    begin
        Str_Error:=Gl_Cls_LocalComm.GetErrorMsg(Result);
        StrPCopy(P_Str_Error,Str_Error);
            Exit;
    end;
end
//Close the communication(External Interface)
function CloseComm():Integer;stdcall;
begin
    Result:=0;
    if not Assigned(Gl_Cls_LocalComm) then
    begin
        Result:=-1;
        Exit;
    end;
    //报内存泄露错误处(释放内存出错)
    FreeAndNil(Gl_Cls_LocalComm);
end；
//-------------------------------Base Comm Class--------------------------------
//Base Creation
constructor TBaseComm.Create();
begin
    Inherited Create();
    Gl_B_ReceivedEnd:=False;
    Gl_B_CheckRecFrameEnd:=False;
end;
//Destroy base class
destructor TBaseComm.Destroy();
begin
    Inherited Destroy();
end;
//------------------------------Local Communication-----------------------------
//initialization the communication
constructor TLocalComm.Create();
begin
    Inherited Create();
    Comm:=TComm.Create(nil);
    Comm.OnReceiveData:=CommReceiveData;
    Gl_B_CheckRecFrameEnd:=False;
end;
//destory and free the comm
destructor TLocalComm.Destroy();
begin
    try
        Comm.StopComm;
        Comm.Free;
    except
    end;
    Application.ProcessMessages;
    Inherited Destroy;
end;
//initialization the comm's prameters
function TLocalComm.InitComm(Str_XML:string):Integer;
begin
    Result:=0;
    Comm.CommName:='//./'+Gl_Str_CommName;
    Comm.BaudRate:=Gl_i_Baudrate;
    Comm.ByteSize:=TEumn_ByteSize[Gl_i_ByteSizeIndex];
    Comm.StopBits:=TEumn_StopBits[Gl_i_StopBitsIndex];
    Comm.Parity:=TEumn_Parity[Gl_i_ParityIndex];
    Comm.ReadIntervalTimeout:=Gl_i_ReadIntervalTimeout;
    //Start
    Comm.Inx_XonXoffFlow:=False;
    Comm.Outx_XonXoffFlow:=False;
    Comm.StopComm;
    try
        Comm.StartComm;
        Sleep(100);
    except
        Result:=con_CommERCode_InitCommFailed;
        Comm.StopComm;
        Exit;
    end;
end;