i have a very strange issue with ajax update panel after i updated he site from asp.net 2.0 to 3.5 (and the ajax control toolkit).


 have a page with a modal popup - modal popup has a update pael with a dropdown list and a text box, when u select a alue in the dropdown it populates the textbox, here is the code:


<asp:Panel ID="Panel1" runat="server" style="display:none; width:350px;" CssClass="modalPopup">
     <asp:UpdatePanel ID="UpdatePanel1" runat="server">
     <ContentTemplate>
 Page: <asp:DropDownList ID="DDLPages" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DDLPages_SelectedIndexChanged">
     </asp:DropDownList><br />
 URL: <asp:TextBox ID="txtpagename" runat="server" Width="320"></asp:TextBox>
                </ContentTemplate>
                </asp:UpdatePanel>
     <asp:UpdateProgress ID="UpdateProgress1" runat="server">
     <ProgressTemplate>
         <asp:Image ID="Image1" runat="server" ImageUrl="~/admin/images/ajax-loader.gif" />
     </ProgressTemplate>
     </asp:UpdateProgress>
                <asp:Button CssClass="subbtn" ID="btncancel" runat="server" Text="Close" />
            </asp:Panel>
    <ajax:ModalPopupExtender ID="ModalPopupExtender2" runat="server" BackgroundCssClass="modalBackground" CancelControlID="btncancel" DropShadow="true" TargetControlID="LinkButton1" PopupControlID="Panel1">
    </ajax:ModalPopupExtender>

also on the page there is an asp panel that i dynamicly load a user control into.

everything was working perfectly when i was using asp.net 2.0 and AJAX.

when i updated the site to use 3.5 ad the newer AJAX tool kit i have noticed a strange error,
depands on the user control loaed the dropdown index chage event that triggers the post back will result in an error: Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500

the debugger shows the error is on:

Sys.Net.XMLHttpExecutor = function Sys$Net$XMLHttpExecutor() {
    /// <summary locid="M:J#Sys.Net.XMLHttpExecutor.#ctor" />
    if (arguments.length !== 0) throw Error.parameterCount();
    Sys.Net.XMLHttpExecutor.initializeBase(this);
    var _this = this;
    this._xmlHttpRequest = null;
    this._webRequest = null;
    this._responseAvailable = false;
    this._timedOut = false;
    this._timer = null;
    this._aborted = false;
    this._started = false;
    this._onReadyStateChange = (function () {
       
        if (_this._xmlHttpRequest.readyState === 4 ) {
            try {
                if (typeof(_this._xmlHttpRequest.status) === "undefined") {
                    return;
                }
            }
            catch(ex) {
                return;
            }
           
            _this._clearTimer();
            _this._responseAvailable = true;
            try {
                _this._webRequest.completed(Sys.EventArgs.Empty);
            }
            finally {
                if (_this._xmlHttpRequest != null) {
                    _this._xmlHttpRequest.onreadystatechange = Function.emptyMethod;
                    _this._xmlHttpRequest = null;
                }
            }
        }
    });