소스는 별문제 없는데요 잘됩니다. 소스 비교해 보시죠
//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
#include "Unit2.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
Form2->Show();
Form2->RichEdit1->Lines->Add(AnsiString().sprintf("Wow!"));
}
//---------------------------------------------------------------------------