<GroupByExpressions>
<telerik:GridGroupByExpression>
<SelectFields>
<telerik:GridGroupByField HeaderText="Classification" FieldName="Classification.Name" ></telerik:GridGroupByField>
</SelectFields>
<GroupByFields>
<telerik:GridGroupByField FieldName="Classification.Name" SortOrder="None"></telerik:GridGroupByField>
</GroupByFields>
</telerik:GridGroupByExpression>
</GroupByExpressions>

<telerik:RadComboBox ID="rcMyCombo" runat="server" CheckBoxes="True" EmptyMessage="Choose ...." Width="300px" DataTextField="Name" DataValueField="Id"
EnableLoadOnDemand="true" ShowMoreResultsBox="true" EnableVirtualScrolling="true" >
<WebServiceSettings Path="http://localhost:8732/MyService.svc" Method="GetDataLoadOnDemand" />
</telerik:RadComboBox>
public RadComboBoxData GetTraderGroupsLoadOnDemand(RadComboBoxContext radComboContext)
{
// my implementation as in the documentation.
}
When i tried to debug the issue using IE debugger tool, i found this is the url that is being called from the web application is the following:
http://localhost:8732/MyService.svc/GetDataLoadOnDemand?context=%5B%7B%22Key%22%3A%22Text%22%2C%22Value%22%3A%22%22%7D%2C%7B%22Key%22%3A%22NumberOfItems%22%2C%22Value%22%3A0%7D%5D&callback=Sys._jsonp0
I'm using VS 2012 and the service is included in my solution so the wcf if not hosted in IIS but the development web server.
Waiting your help and support.
Appreciate it.

<telerik:RadGrid ID="SequenceGrid" runat="server" AllowPaging="True" PageSize="10" GridLines="None" AllowFilteringByColumn="false" AllowSorting="True" Skin="Sunset" TabIndex="13" AllowMultiRowSelection="true" > <PagerStyle AlwaysVisible="true" Position="Bottom" /> <MasterTableView AutoGenerateColumns="False" DataKeyNames="id, testCaseGroupInd" ClientDataKeyNames="id, TCStatusColor, StatusColor, Tags, testCaseGroupInd, SeqName" Width="100%"> <%--TableLayout="Fixed"--%> <Columns> <telerik:GridBoundColumn DataField="id" HeaderText="ID" SortExpression="id" UniqueName="id"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" Width="50px" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="SeqName" HeaderText="Name" SortExpression="SeqName" UniqueName="Sequence"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="TestCaseStatus" HeaderText="Test Case / Group Status" SortExpression="TestCaseStatus" UniqueName="test_case_status"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="Uploaded" HeaderText="Uploaded" UniqueName="upload_status"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="CreatedBy" HeaderText="Created By" SortExpression="CreatedBy" UniqueName="created_by"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="ModifiedBy" HeaderText="Last Modified By" SortExpression="ModifiedBy" UniqueName="last_modified_by"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="Project" HeaderText="Project" SortExpression="project" UniqueName="project"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn HeaderText="Tags" DataField="id" UniqueName="tag_link" SortExpression="Tags" > <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridBoundColumn DataField="ExecutionTime" HeaderText="Scheduled Run Time" SortExpression="ExecutionTime" UniqueName="execution_time"> <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" ForeColor="White" /> </telerik:GridBoundColumn> <telerik:GridButtonColumn Display="false" HeaderStyle-Width="20px" UniqueName="AddToGroup" ButtonType="ImageButton" CommandName="AddToGroup" Text="Add to Group" ImageUrl="~/Images/AddRecord.png" > </telerik:GridButtonColumn> </Columns> </MasterTableView> <ClientSettings AllowColumnsReorder="false" AllowRowsDragDrop="True" > <Selecting AllowRowSelect="True" EnableDragToSelectRows="True" /> <%--<Scrolling AllowScroll="true" EnableVirtualScrollPaging="true" UseStaticHeaders="true" />--%> <DataBinding SelectMethod="GetDataAndCount" Location="AutomationDeck.svc" SortParameterType="String" FilterParameterType="String" /> <ClientEvents OnDataBound="SequenceGrid_OnDataBound" OnDataBinding="SequenceGrid_OnDataBinding" OnRowContextMenu="RowContextMenu" OnDataBindingFailed="SequenceGrid_OnDataBindingFailed" OnCommand="SequenceGrid_Command" OnRowDropping="GroupItemsGrid_onRowDropping" OnRowDragStarted="GroupItemsGrid_OnRowDragStarted" /> </ClientSettings></telerik:RadGrid>function collapse() { var SeqGrid = $telerik.findGrid("<%= SequenceGrid.ClientID %>"); SeqGrid.get_masterTableView().hideColumn(2); SeqGrid.get_masterTableView().hideColumn(3); SeqGrid.get_masterTableView().hideColumn(4); SeqGrid.get_masterTableView().hideColumn(5); SeqGrid.get_masterTableView().hideColumn(6); SeqGrid.get_masterTableView().hideColumn(7); SeqGrid.get_masterTableView().hideColumn(8); SeqGrid.get_masterTableView().showColumn(9);} function expand() { var SeqGrid = $telerik.findGrid("<%= SequenceGrid.ClientID %>"); SeqGrid.get_masterTableView().hideColumn(9); SeqGrid.get_masterTableView().showColumn(2); SeqGrid.get_masterTableView().showColumn(3); SeqGrid.get_masterTableView().showColumn(4); SeqGrid.get_masterTableView().showColumn(5); SeqGrid.get_masterTableView().showColumn(6); SeqGrid.get_masterTableView().showColumn(7); SeqGrid.get_masterTableView().showColumn(8); }