index change is not firing post back even though autopostback is set to true

hi here is myfront end related
<tr class="TRArea3"> <td class="TDSpacer"> </td> <td class="TDLabel"> Replacement<asp:Label ID="Label12" runat="server" EnableViewState="False" SkinID="lblStar" Text=" *"></asp:Label></td> <td class="TDText"> <asp:RadioButtonList ID="rblreplac" AutoPostBack="true" runat="server" OnSelectedIndexChanged="rblreplac_SelectedIndexChanged" RepeatDirection="Horizontal"> <asp:ListItem Value="True" Text="Yes"></asp:ListItem> <asp:ListItem Value=" ...