Unmodified DropDownList in UpdatePanel causes Event Validation error in FireFox

Background

I have an ASP.net UserControl that is a simple user input form. It uses an UpdatePanel and UpdaetProgress to display a "working" gif after they click submit. We have gotten reports that the submit button sometimes doesn't do anything in FireFox, IE 8, and Safari. When looking into that, I couldn't reproduce any problems in IE, but found that in FireFox, the submit button got the following script error which was preventing the postback:

Error: Sys.WebForms.PageRequestManagerServerErrorException: Invalid postback or callback argument.  Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
Source File: http://localhost:1127/ScriptResource.axd?d=ZYU-uPMJ_AcQgBrmkW_WO13JlNZSAb9cMptxJsQIH1LnA8NC31pa7PAk8l5lYCB8LDDwft7xwh7Z107MKgt7KHHBeQaeEncnAFKLJ04CaHgelsuOOv072-1ZBvMW7N_x0&t=3693a5e0
Line: 1111

Problem

To figure out what was causing the error, I gradually whittled down my code until I had almost nothing left. What I found was that when I select from a DropDownList in an UpdatePanel, the button gets this error (in FireFox only). If I remove the DropDownList, don't make a selection, or remove the UpdatePanel, the submit button posts back correctly (any 1 of those).

Example

Create an ASP.net 3.5 project and place the code below in an aspx page. Set a break point in your Page_Load or OnClick event handler in the code behind. Run it, make a selection from the DropDownList and then ClickSubmit. Notice the breakpoints are not hit.

<form id="form1" runat="server">
    <div>
        <asp:ScriptManager runat="server">
        </asp:ScriptManager>
        <div id="Div1" class="form-layout membership payment">
            <asp:UpdatePanel ID="UpdatePanel1" runat="server" RenderMode="Inline">
                <contenttemplate>
                    <table cellpadding="0" cellspacing="0" border="0" class="form_table payment">
                        <tr>
                            <th align="right" valign="top">
                                State <span class="reqd">*</span>
                            </th>
                            <td>

                                <asp:DropDownList Width="75px" ID="ddlState" CssClass="txt" runat="server" AutoPostBack="false">
                                    <asp:ListItem Value="" Text="--Select--" />
                                    <asp:ListItem>AB
                                    </asp:ListItem>
                                    <asp:ListItem>AL
                                    </asp:ListItem>
                                </asp:DropDownList>
                            </td>
                        </tr>
                    </table>
                    <div class="clear-left pad-bottom">
                    </div>
                    <asp:Label ID="lblCreditCardError" CssClass="creditCardError" runat="server">
                    </asp:Label>
                    <table cellpadding="0" cellspacing="0" border="0" class="form_table">
                        <tr>
                            <th align="right" valign="top">
                            </th>
                            <td>
                                <asp:HiddenField ID="HFSubmitForm" runat="server" Value="0" />
                                <asp:Button ID="btnTest" runat="server" OnClick="btnSubmitCC_Click" />
   开发者_开发百科                         </td>
                        </tr>
                    </table>
                </contenttemplate>
            </asp:UpdatePanel>
        </div>
    </div>
</form>

I don't think using markup should matter anyway, but I tried adding the items to the DropDownList using binding in an if(!IsPostBack) block in the Page_Load method, but it didn't change anything.

---

I'm not sure if this causes your issue, but try to format the DropDownList-Items correctly:

<asp:DropDownList Width="75px" ID="ddlState" CssClass="txt" runat="server" AutoPostBack="false">
     <asp:ListItem Text="--Select--"></asp:ListItem>
     <asp:ListItem Text="AB"></asp:ListItem>
     <asp:ListItem Text="AL"></asp:ListItem>
</asp:DropDownList>

---

First off, you are missing this under your UpdatePanel:

<Triggers>
    <asp:AsyncPostBackTrigger ControlID="btnTest" />
</Triggers>

Second... either bind the list options in code-behind, turn off event validation for this page, or call RegisterForEventValidtion() for each of your options, I believe. I'm a little sketchy on this last one since I've never really used it. I was able to get your code working by simply adding the AsyncPostBackTrigger and then binding the DDL in code-behind.

Finally, it's possible that you are simply missing these unhandled exceptions while debugging because you are expecting something from the browser... but really it should appear to the browser that nothing has happened. Pull up EventViewer to see unhandled ASP.NET exceptions. The exception is stopping execution before you get the event handler.

---

@Tim Schmelter- Ahhh that explains it. (Replying in an answer so I can show code and make sure your answer is clear) Here's what ASP.NET sends to the browser:

<SELECT style="WIDTH: 75px" id=ddlState class=txt name=ddlState> 
    <OPTION selected value="">--Select--</OPTION> 
    <OPTION value="AB&#13;&#10;                                    ">AB</OPTION> 
    <OPTION value="AL&#13;&#10;                                    ">AL</OPTION>
</SELECT>

&#l3;&#l0 is /r/n. In IE, this whole value displayed above is included in the HTML, but in FireFox it's reduced down to a single space (e.g. "AB "). When it's passed back to the server it sees the selected option's value is not one that was originally included. I had compared the HTML sent to what was in FireFox but I looked at the above HTML in Visual Studio's XML Visualizer which also removed them so I didn't notice the difference.