If the error about _itemDrag says it is not defined, it means you haven't enabled ItemsDragDrop in RadListView. RadListView's client-object has a field named _itemDrag that refers to another client object implementing drag-and-drop for listview items. This object is added to the listview client object only when items-drag-and-drop is enabled. Therefore, if you do not have it, most probably you haven't enabled drag-and-drop. It is also important to mention that RadListView's drag-and-drop functionality is available since version 2010.Q1 of Telerik RadControls for ASP.NET AJAX. If you happen to be using an older version, drag-and-drop is not available.
Also, note that to make your items draggable, you need to indicate the listview item's boundaries. As RadListView does not define and track its own HTML elements, it is the developer's responsibility to indicate which HTML element is the RadListView DataItem container. This is done using the .rlvI and .rlvA CSS classes applied to your listview container elements as indicated in the demo and help article we referred to in previous posts. Failing to put .rlvI or .rlvA classes to your item HTML elements will prevent them from being dragged.
Finally, when dropping a RadListView item on the page, the immediate target HTML element's id is sent to the server. This client ID is available in the ItemDrop event's DestinationHtmlElement property. You need to use it to indicate the the destination category, meaning the client ID of your HTML element should contain information about the target category, which you need to use on the server.
Finally, the TrackManager you asked about is a custom class in the RadListView Items drag-and-drop demo. It simply helps abstract data operations like getting all tracks in a single category, getting all categories, as well as setting the category for a specified track.
I hope things are clearer now. If you have any specific questions, please ask.
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