Modal dialog handling

Hi,
I’m using watir 182(the version that supports modal dialog) to automate
a test.there is this pop up modal dialog where I have to click on
checkbox to choose an interval. rightnow seems it could not even detect
the existence of this modal dialog.
is there any other way I could identify it, e.g. id or name?

if($ie.modal_dialog(:title,“Intervals – Webpage Dialog”).exists?)
then
puts “dialog found”
end

thanks