AFAIK, to close Excel application you have to create it via CoCreateInstance

It's published and available in pdf (try google)

May be You enter too long data

The simplest way is to restart Internet Explorer

m_pDC and m_pBitmap are not initialized. Try

CDC *m_pDC = new CDC();
CBitmap* m_pBitmap = new CBitmap();

m\_pDC->CreateCompatibleDC(pInputDC);
m\_pBitmap->CreateCompatibleBitmap(pInputDC, width, height);
m\_pDC->SelectObject(m\_pBitmap);
m\_pDC->Rectangle(0,0,width,height);

You have to add this two functions to the end of your interface

You already have messsage loop Why do you call

CAuthenticationAddin::TabPageMessageLoop (m_lptc->hTabPages[currentSel]);

Try to comment all calls to it

GetModuleFileName(NULL, szPath, MAX_PATH);
CreateService(schSCManager, USER_SERVICE_NAME, USER_SERVICE_NAME, SERVICE_ALL_ACCESS,SERVICE_WIN32_OWN_PROCESS,SERVICE_DEMAND_START,SERVICE_ERROR_NORMAL, szPath, NULL, NULL, NULL, NULL, NULL);

Try register service from another process

Can You list all code ? Mey be you do not need this messgae loop. May be you need only Tab WndProc.