I have developed an ASP.NET Dynamic Data site that also contains some custom pages using the DD features.

 The site has been working fine for weeks, but all of a sudden this morning on one Page I am receiving the error:

Sys.WebForms.PageRequestManagerServerErrorException: Invalid postback or callback argument. ...

This happens when I try and click the Next or Last button or try and change the page number on a asp:GridViewPager supplied as part of DD.  This page has been working fine with multiple pages up until today.

This system is now live, so I would love any help or direction you can provide.  Code inline below:

Default.aspx:

<%@ Page Language="C#" MasterPageFile="~/Requests.master" CodeFile="Default.aspx.cs" Inherits="ListRequests" %>


<%@ Register src="~/DynamicData/Content/GridViewPager.ascx" tagname="GridViewPager" tagprefix="asp" %>
<%@ Register src="~/DynamicData/Content/FilterUserControl.ascx" tagname="DynamicFilter" tagprefix="asp" %>


<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <asp:DynamicDataManager ID="DynamicDataManager1" runat="server" AutoLoadForeignKeys="true" />


    <h2>Your Virtual Server requests</h2>
    <p>Only requests for user <asp:Label ID="labelUser" runat="server" Font-Bold="True" /> are show below.</p>
    <p>Use the search function to find requests you did not submit.</p>
    <asp:ScriptManagerProxy runat="server" ID="ScriptManagerProxy1" />


    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:ValidationSummary ID="ValidationSummary1" runat="server" EnableClientScript="true"
                HeaderText="List of validation errors" />
            <asp:DynamicValidator runat="server" ID="GridViewValidator" ControlToValidate="GridView1" Display="None" />


            <asp:GridView ID="GridView1" runat="server"
                AllowPaging="True" AllowSorting="True" CssClass="gridview">
                <Columns>
                

                    <asp:TemplateField>
                        <ItemTemplate>
                            <asp:HyperLink ID="DetailsHyperLink" runat="server"
                                NavigateUrl='<%# "/VRM/requests/ViewRequest.aspx?id=" + Eval("Request_id") %>'
                                Text="Details" />
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>


                <PagerStyle CssClass="footer"/>
                <PagerTemplate>
                    <asp:GridViewPager runat="server" />
                </PagerTemplate>
                <EmptyDataTemplate>
                    You have not yet submitted any requests.
                </EmptyDataTemplate>
            </asp:GridView>
            <br />
        </ContentTemplate>
    </asp:UpdatePanel>
</asp:Content>

 Default.aspx.cs

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml.Linq;
using System.Web.DynamicData;

public partial class ListRequests : System.Web.UI.Page {
    protected void Page_PreInit(object sender, EventArgs e)
    {
        this.MasterPageFile = AppHelpers.DynamicMaster();
    }
    
    protected void Page_Init(object sender, EventArgs e) {
        DynamicDataManager1.RegisterControl(GridView1, true /*setSelectionFromUrl*/);
    }

    protected void Page_Load(object sender, EventArgs e) {
        VRMDataContext db = new VRMDataContext();
        var rows = from p in db.Requests
                   where p.RequesterLogon.Equals(AppHelpers.CurrentUser())
                   orderby p.RequestDate descending
                   select new
                   {
                       Request_ID = p.id,
                       Server_Name = p.ServerName,
                       Date_Requested = p.RequestDate,
                       Stage = p.RequestStage.Name,
                       Environment = p.Environment.Name,
                       Location = p.Location.Name,
                       PU = p.PUperCPU,
                       CPUs = p.NumCPUs,
                       Replicated = p.Replicated,
                       LUN = p.LUNsize
                   };


        GridView1.DataSource = rows;
        GridView1.DataBind();
        labelUser.Text = AppHelpers.CurrentUser();

    }

    protected void OnFilterSelectedIndexChanged(object sender, EventArgs e) {
        GridView1.PageIndex = 0;
    }
}