Fejlmeddelelse v/ "closefile(F)" ved downloadning af fil via HTTP

Hej,

jeg får en fejlmeddelelse i næst nederste kodelinie "CloseFile(F)" - Hvad gør jeg galt...??

function TMainFunctionForm.DownloadURL(const aUrl: string): Boolean;
var
  hSession: HINTERNET;
  hService: HINTERNET;
  lpBuffer: array[0..1024 + 1] of Char;
  dwBytesRead,akk,dwindex,dwcodelen: DWORD;
  LocalFile:string;
  F : File;
  filesize : DWord;
  dwcode:pointer;
  res : pchar;
begin
  Result := False;
  LocalFile := 'C:\akljsdh.avi';
  Assignfile(F,LocalFile);
  Rewrite(F,1);
  akk := 0;
  dwcodeLen := 20;
  dwIndex := 0;
  hSession := InternetOpen('alds', INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);

  try
    if Assigned(hSession) then
    begin
      hService := InternetOpenUrl(hSession, PChar(aUrl), nil, 0, INTERNET_FLAG_RELOAD, 0);
      HttpQueryInfo(hService, HTTP_QUERY_CONTENT_LENGTH, @dwcode, dwcodeLen, dwIndex);
      res := pchar(@dwcode);
      edit1.text := res;
      filesize := StrToInt(res);
      if Assigned(hService) then
      begin
        Application.processmessages;
        try
          while True do
          begin
            dwBytesRead := 1024;
            InternetReadFile(hService, @lpBuffer, 1024, dwBytesRead);
            BlockWrite(F, lpbuffer, dwBytesRead);
            if dwBytesRead = 0 then break;
            akk := akk + dwBytesRead;
            Application.ProcessMessages;
            ProgressBar1.Position := Round(akk/filesize * 100);
          end;
          Result := True;
        finally
          InternetCloseHandle(hService);
        end;
      end;
    end;
  finally
    InternetCloseHandle(hSession);
  end;
  CloseFile(F);
end;