OraQuery1: Cannot perform this operation on an closed dataset

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "ServerMainForm.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma link "DBAccess"
#pragma link "MemDS"
#pragma link "Ora"
#pragma link "OraCall"
#pragma link "OraSmart"
#pragma link "OraProvider"
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
    OraQuery4->SQL->Text = "select First_Name from employees";
    OraQuery4->Open();
    ComboBox1->Clear();
    OraQuery4->First();
 
        for (int i=0; i < OraQuery4->RecordCount; i++) {
            ComboBox1->Items->Add(OraQuery4->Fields->Fields[0]->AsString);
            OraQuery4->Next();
        }
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::ComboBox1Change(TObject *Sender)
{
    s1 = (ComboBox1->Items->Strings[ComboBox1->ItemIndex]);
 
    OraQuery4->SQL->Text = "select employee_id from Employees where First_Name = '" + s1 + "'";
    OraQuery4->Open();
 
    Label4->Caption = OraQuery4->Fields->Fields[0]->AsString;
}
//---------------------------------------------------------------------------
 
 
 
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
    //загрузка dll
    HINSTANCE DLL = LoadLibrary(L"TestDLL.dll");
 
    //проверка загрузки
    if (DLL)
    {
        LoadSayFunction = (SayType *)GetProcAddress(DLL, "_Say");
        if (LoadSayFunction)
            LoadSayFunction("Dynamic Hello");
        else
            ShowMessage(SysErrorMessage(GetLastError()));
        FreeLibrary(DLL);
    }
    else {
        ShowMessage(SysErrorMessage(GetLastError()));
        ShowMessage("Unable to load the DLL");
        //модуль не загрузился
    }
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button2Click(TObject *Sender)
{
    S1 = Edit1->Text;
    S2 = Label4->Caption;
 
    OraQuery4->SQL->Text = "update employee_history set department = '" + S1 + "' where employee_id = " + S2;
    OraQuery4->ExecSQL();
 
    OraQuery1->ExecSQL();
    OraQuery2->ExecSQL();
    OraQuery3->ExecSQL();
}
//---------------------------------------------------------------------------
 
 
 
 
void __fastcall TForm1::Button3Click(TObject *Sender)
{
    OraQuery1->ApplyUpdates();
    OraQuery1->CommitUpdates();
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button4Click(TObject *Sender)
{
    OraQuery1->CancelUpdates();
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::FormCloseQuery(TObject *Sender, bool &CanClose)
{
    if (OraQuery1->CachedUpdates)
        switch (Application->MessageBox(L"Save changes",L"Accept changes", MB_YESNOCANCEL + MB_ICONQUESTION))
        {
            case IDYES: OraQuery1->ApplyUpdates();
                 break;
            case IDCANCEL: CanClose = false;
                 break;
            case IDNO: OraQuery1->CancelUpdates();
        }
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::CheckBox1Click(TObject *Sender)
{
    OraQuery1->CachedUpdates = ! OraQuery1->CachedUpdates;
    Button3->Enabled = OraQuery1->CachedUpdates;
    Button4->Enabled = OraQuery1->CachedUpdates;
}
//---------------------------------------------------------------------------
 
 
 
void __fastcall TForm1::OraQuery1BeforePost(TDataSet *DataSet)
{
    if (Application->MessageBox(L"Want to extract in DB?",L"Accept extract in DB", MB_YESNOCANCEL + MB_ICONQUESTION) != IDYES) {
        DataSet->Cancel();
        Abort();
    }
    else {
        Application->MessageBox(L"Error data",L"Error", MB_ICONSTOP);
        Abort();
    }
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::FormCreate(TObject *Sender)
{
   OraQuery1->Active = true;
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::FormDestroy(TObject *Sender)
{
    OraQuery1->Active = false;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)
{
   OraQuery1->Active = true;
 
}

void __fastcall TForm1::CheckBox1Click(TObject *Sender)
{
    if (CheckBox1->Checked) {
        Button3->Enabled = OraQuery1->CachedUpdates;
        Button4->Enabled = OraQuery1->CachedUpdates;
        if (OraQuery1->CachedUpdates) {
            OraQuery1->Active = true; modif = false;
        }
    }
    else {
        Button3->Enabled = false;
        Button4->Enabled = false;
        OraQuery1->Active = false;
    }
}