If you are programming directly to the Windows API, you must handle the message from the MobiLink provider in your application's WindowProc function, using the ULIsSynchronizeMessage function to determine if it has received the message.

Here is an example of how to handle the message:

LRESULT CALLBACK WindowProc( HWND hwnd,
         UINT uMsg,
         WPARAM wParam,
         LPARAM lParam )
{
  if( ULIsSynchronizeMessage( uMsg ) ) {
    DoSync();
    if( wParam == 1 ) DestroyWindow( hWnd );
    return 0;
  }
  switch( uMsg ) {
  // code to handle other windows messages
  default:
    return DefWindowProc( hwnd, uMsg, wParam, lParam );
  }
  return 0;
}

where DoSync is the function that actually calls ULSynchronize.

See ULIsSynchronizeMessage function.