SetTimer not working

Hello,

I have a welcome dialog which registers my users to a web server just after
the application is installed. This registragion may take from 5 to 30
seconds:

void CWelcomeDlg::OnBnClickedOK()

{

    DoLengthyProcessing();

    this->EndDialog(1);

}

As I said, the processing takes long to finish, so I wanted to show a
feedback to my users that the program hasn't stopped working. I inserted a
Static control and implemented a simple animation:

void CWelcomeDlg::OnTimer(UINT_PTR nIDEvent)

{

    CStatic* pLabel = (CStatic*)GetDlgItem(IDC_LBL_PROCESSING);

    CString strVal;

    pLabel->GetWindowText(strVal);

    if (strVal == L"/")

        pLabel->SetWindowTextW(L"\\");

    else if (strVal == L"\\")

        pLabel->SetWindowTextW(L"/");

    CDialog::OnTimer(nIDEvent);

}

and changed the previous click event shown before to start the timer:

 void CWelcomeDlg::OnBnClickedOK()

{

    m_nTimer = SetTimer(1, 1000, NULL);

    DoLengthyProcessing();

    KillTimer(m_nTimer);

    this->EndDialog(1);

}

The problem is the timer isn't working while the lengthy procesing is
running. If I put the SetTimer() and KillTimer() inside the click event of
two command buttons, it works fine.

The processing connects with a Windows Service via named pipe, and the
Windows Service makes the needed registration via web.

Why the timer isn't working? How can I do the same if not with timer?

I tried moving the lengthy processing into a thread and kept the timer in
the main thread, but it not worked as well.

Please help.

Jeova