Ошибка при вызове функции из dll

//---------------------------------------------------------------------------
#include <vcl.h>
#include <windows.h>
#include "TestSum.h"
#pragma hdrstop
extern "C++" void DLL_EI Sum(TEdit, TEdit, TLabel);
 
#pragma argsused
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fwdreason, LPVOID lpvReserved)
{
    return 1;
}
 
void Sum(TEdit *Edit, TEdit *Edit2, TLabel *Label)
{
    float a, b, c;
 
    a = StrToFloat(Edit1->Text);
    b = StrToFloat(Edit2->Text);
 
    c = a + b;
 
    Label->Caption = c; 
}
//---------------------------------------------------------------------------

#ifndef _TESTSUM_H
#define _TESTSUM_H
 
#ifdef __DLL__
#define DLL_EI __declspec(dllexport)
#else
#define DLL_EI __declspec(dllimport)
#endif
extern "C++" void DLL_EI Sum(TEdit, TEdit, TLabel);
#endif

//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop
 
#include "code.h"
#include "TestSum.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
#pragma link "Sum.lib"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    Sum(Edit1, Edit2, Label1);
}
//---------------------------------------------------------------------------