MultiItem Selection Not Working

I've a RadComboBox which is filled by a webservice something like this 

   <telerik:RadComboBox   CheckBoxes="true"

                SelectionMode="Multiple" ShowCheckAll="true" ID="WorkStreamID" runat="server"
                Height="100" Width="150" EmptyMessage="Select Team" EnableLoadOnDemand="true"
                WebServiceSettings-UseHttpGet="true"  >
                               <ClientItemTemplate>                                 
                            <b>#= Text # </b>
                            </ClientItemTemplate>
                <WebServiceSettings Method="GetWorkStream" Path="~/ProjectDropDownWebService.asmx" />
            </telerik:RadComboBox>​

and I want to get selected values of this combo inside button submit event 

 foreach (RadComboBoxItem item in WorkStreamID.CheckedItems)
        {
            //It never gets in here it says no checked items
        }​

I want to get checked items list but its not working.. I think my combo is filled from web service that's causing the problem may be.