Dropdown list in updatepanel on IIS 7 stuttering?

Hi all,

I created a site in VS2010 that uses a dropdownlist to select an item. When the user selects the item, other fields are populated based on that selection. I tested this on a dev server running IIS 5 and IIS 6 (2 servers) and each worked great. As soon as the user made the selection, the code fired and the fields were updated.

So now I am trying in on IIS 7. What's odd is the first time I select the item, nothing happens. If I select a different item AFTER I select an item everything fires. Very strange.

The basic code is below:

Code:

---

    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="ddlItemCode" />
            <asp:AsyncPostBackTrigger ControlID="ddlLotCode" />
            <asp:AsyncPostBackTrigger ControlID="ddlWarehouse" />
            <asp:AsyncPostBackTrigger ControlID="btnSubmit" />
        </Triggers>
        <ContentTemplate>
.
.
.
                  <tr>
                        <td><asp:DropdownList ID="ddlItemCode" runat="server" OnSelectedIndexChanged="ddlItemCode_Select" AutoPostBack="true"></asp:DropdownList></td>
                        <td><asp:Literal ID="litDescription" runat="server"></asp:Literal></td>
                        <td><asp:DropdownList ID="ddlLotCode" runat="server" OnSelectedIndexChanged="ddlLotCode_Select" AutoPostBack="true"></asp:DropdownList></td>
                        <td><asp:DropdownList ID="ddlWarehouse" runat="server"></asp:DropdownList></td>
                        <td><asp:Literal ID="litAvailableQty" runat="server"></asp:Literal></td>
                        <td><asp:TextBox ID="txtPickAmount" runat="server"></asp:TextBox></td>
                        <td><asp:Literal ID="litErrorMessage" runat="server" Visible="false"></asp:Literal><asp:Button ID="btnSubmit" runat="server" Text="Pick Item"
                                onclick="btnSubmit_Click"/></td>
                    </tr>
.
.
.

---

Any ideas as to why the first seelction does nothing but subsequent selections fire?

I discovered something. On the screen I am using the ajax calender extender. If I don't click on the calender icon to enter the date, it works perfectly. But if I click on the calender icon and enter the date, then I have the issue. The calender extender is OUTSIDE of the update panel.