I had exactly the same issue with a CrossTab. If you have a look at this thread
you'll see what I tried and how I got it to work.
In the same thread, one of the clever chaps from telerik towers posted about how we should
be trying to do it.
Steve@telerik points to this help article
but I guess I lack the relevant Masters degree in WTF! 'cos I couldn't follow i. If you can make head or tail of the 'scope' stuff, please post you thoughts here.