sys.extended.ui is null or not an object sharepoint

I'm working in SharePoint 2010 and using ajax toolkit 3.0.30930.28736

I'm using the ajax toolkit slider control. For some reason I wanted to override the following method of slider

 Sys.Extended.UI.SliderBehavior.prototype._getNearestStepValue

But on this statement it gives me following error

sys.extended.ui is null or not an object

I saw some forums where people suggested to set CombineScripts="false" in my ajax toolkit based script manager which I did

<ajaxToolkit:ToolkitScriptManager ID="tsm"  runat="server" CombineScripts="false" EnablePartialRendering="true" 
         LoadScriptsBeforeUI="true"></ajaxToolkit:ToolkitScriptManager>

but still facing this issue. Why am I unable to have Sys.Extended object?