The problem is in the way you register the ClientValueChange handler for each RadSlider. When you click the button and thus initiate a postback, your code in the CoreCompetencyRadGrid_ItemDataBound will not be executed as the RadGrid is already bound. Thus, you will not register the client script and all ClientValueChange handlers are lost. As you do not have those defined after the postback, the initialization of all RadSliders will fail.
Having said that, you need to find a way to define all ClientValueChange handlers so that those will be available after postback and callback. For example - define one handler for all RadSliders and based on the ClientID of the RadSlider, find the corresponding Label.
In case you would like to use your approach, that is, define a different handler for each slider, you can use the ItemCreated event, instead of the ItemDataBound event, as it is raised after postback as well.
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