Application freezes after ShellExecuteEx

Hi all.

After the execution of this function (which I use to merge a .reg file into the Windows registry), application freezes: the file is merged I see the usual prompts which ask for merging file and confirming the merging has been successful, then The Explorer window when I started my app brings to front and my application can't get focus.

Any idea?

function TfrmMain.RunAsAdmin(hWnd: HWND; aFile,
  aParameters: String): Boolean;
var
  sei: TShellExecuteInfo;
  ExitCode: DWord;
begin
  Result := False;
  FillChar(sei, SizeOf(sei), 0);
  sei.cbSize := SizeOf(sei);
  sei.Wnd := hWnd;
  sei.fMask := SEE_MASK_NOCLOSEPROCESS or SEE_MASK_UNICODE;
  sei.lpFile := PChar(aFile);
  sei.lpParameters := PChar(aParameters);
  sei.nShow := SW_SHOWNORMAL;
  if ShellExecuteEx(@sei) then
  begin
     repeat
       Application.ProcessMessages;
       GetExitCodeProcess(sei.hProcess, ExitCode) ;
     until (ExitCode <> STILL_ACTIVE) or
                        Application.Terminated;
     result := True;
  end;
end;

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Thanks to all in advance.
Marco