I have observed that if we change the focus (from the slide show) while running a slide show, which is set to advance automatically (in a secondary monitor) the slide show pauses automatically.
Actually, I didn't know about this untill I did a slide show for a function and it ruined that slideshow. First I thought it was a compatibility issue because I prepared the slides in Office 2007 and I used Office 2010 to present it, later I ruled out that possibility (because Office is backward compatible, not sure about this).
After carefully analysing what I did at the function, I could found that the slide show paused because I shifted the focus from slide show to do another works in the pc. I confirmed my theory/point after visiting this page.
There is a work around given in that page, but it is for Office 2003.
Would anyone care to explain how to solve this issue in Office 2007, 2010 etc(with pictures, if you don't mind).