scriptaculous slider problem

I am trying to create a slider,
Here is my CSS:

.track {
   background-color: #aaa;
   position: relative;
   height: 0.5em; width: 10em;
   cursor: pointer; z-index: 0;
}
.handle {
   background-color: red;
   position: absolute;
   height: 1em; width: 0.25em; top: -0.25em;
   cursor: move; 
   z-index: 2;
}

Code (markup):

My HTML:

		<div id="track_Size" class="track">
			<div id="handle_Size" class="handle"></div>
		</div>

HTML:

My script:

Control[0]=new Control.Slider('handle_Size','track_Size');

Code (markup):

I keep getting "this.track is null", error is thrown by scriptaculous.
Can anybody help me out here?