SelectedValue of RadComboBox is not updated

[abasi]

I have a RadComboBox inside a RadXmlHttpPanel.In the ServiceRequest method i set the selectedvalue of the combobox to a new value but the selectedvalue is not updated.

<telerik:RadXmlHttpPanel ID="mainRadXmlHttpPanel" runat="server" OnServiceRequest="main_ServiceRequest"
  RenderMode="Block" LoadingPanelID="RadAjaxLoadingPanel1" EnableClientScriptEvaluation="true"                     Width="117%">
<telerik:RadComboBox ID="mainShipCb" runat="server" Width="150px"> </telerik:RadComboBox>
 </telerik:RadXmlHttpPanel>

CodeBehind :

protected void main_ServiceRequest(object sender, RadXmlHttpPanelEventArgs e)
   {
        mainShipCb.SelectedValue = "Some Value";

   }