Hi Paul,
In order to make cascading ComboBoxes, you should initiate an ajax request in order to add items to the second ComboBox. This should be implemented using the
ajaxRequest method of the RadAjaxManager's client-side object. As an argument you should pass the value based on which items will be loaded. Also you should add specific ajax settings as shown below:
I hope this would help.
All the best,
Dimitar Terziev
the Telerik team