Timer tick event does not fire in second user control

I've run into a problem with one of my web sites and I am having trouble figuring out the problem and a good solution.  This is my scenario:
I have a user control that displays a slideshow with images and some text that changes every fifteen seconds.  To do this, I have an update panel that contains a timer control with an interval of 15000.  It calls a method called slideshowTimer_Tick in the codebehind.  The web page that contains this user control is a relatively simple page; no update panels or timers, just divs.
The problem I have is that if I have two of these user controls on the page, the tick event only fires for the first control.  It never fires for the second control, although the control is full initialized otherwise.
Any ideas?
Thanks
Michael
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