I'm using Telerik SL4 (2009 3 1314 1030) RadGridView with RIA Services, EF 4.0 and an MS SL4 DataPager. I set the initial RIA sort descriptors in the xaml but these can be overwritten by clicking on any given grid column header. An RIA error occurs when the user by clicking on a header changes that column's sort descriptor to None. The reason for this error is the Telerik grid removes all sort descriptors from the DDS. The RIA service and EF requires that the DDS has at least one sort descriptor when its used in conjunction with a DataPager. This error can be avoided if when handling the DDS' OnDataLoading event it is verified that there is at least one SortDescriptor set before fetching more data for a new page. The main problem with this is the page in view when the user specified the 'None' sort descriptor is unsorted but all other pages are sorted per the descriptor supplied in the OnDataLoading handler. I tried to resolve this by creating a grid sorting event handler that changes a sort descriptor from none to a descriptor equivalent to the one assigned the DDS in the DataLoading handler so even the initial page is sorted.
The best solution would be for Telerik to allow client side sorting to be configured to disallow the 'None' sort descriptor. Second best allow the grid sorting handler to pre-empt the selection of a 'None' sort descriptor.
Currently the best solution is to block client side sorting altogether.