Combobox selected item is deleted once selected . Invalid Postback or Callback argument
<p>I have four textboxes one combobox and one button ( and some other controls) in my page . Based on the values typed in the textboxes the related values are updated in the  combobox. On clicking the submit button in my page It was giving the following error .</p>

<blockquote>
  <blockquote>
    <p>"Invalid postback or callback argument. Event validation is enabled using in configuration or in a page. For Secuity 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 <code>ClientScriptManager.RegisterForEventsValidation</code> method in order to register the postback or callback data for validation."</p>
  </blockquote>
</blockquote>

<p>Now in the page directive I added </p>

<pre><code>&lt;%@Page EnableEentValidation="false"&gt; 
</code></pre>

<p>When I type the values in the four  textboxes the corresponding value will appear in the cobobox . But when I select that combobox value, the selected value wil be deleted . What is the reason for this ?</p>

<pre><code>&lt;%@ Page Language="C#" MasterPageFile="~/Main.Master" AutoEventWireup="true" CodeBehind="AddeChecklist.aspx.cs"
    Inherits="LabTrack.WebApplication.Echecklist.AddeChecklist" EnableEventValidation ="false" %&gt;

&lt;%@ Register TagPrefix="Labinal" TagName="AutoCompleteControl" Src="~/UserControls/AutoCompleteEnabledWebUserControl.ascx" %&gt;
&lt;asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server"&gt;
    &lt;link href="../Styles/CheckListRev.css" rel="stylesheet" type="text/css" /&gt;
    &lt;!-- Style for the page --&gt;
    &lt;link href="../Styles/AddeChecklist.css" rel="stylesheet" type="text/css" /&gt;
&lt;/asp:Content&gt;
&lt;asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server"&gt;
    &lt;asp:ScriptManager ID="ScriptManager1" EnablePartialRendering="true" runat="server"&gt;
    &lt;/asp:ScriptManager&gt;
    &lt;asp:Panel ID="ErrorMessagePanel" CssClass="ErrorPanel" Visible="true" runat="server"&gt;
        &lt;div class="ErrorDiv"&gt;
            &lt;asp:BulletedList CssClass="ErrorMessage" ID="ErrorMessageBulletedList" runat="server"&gt;
            &lt;/asp:BulletedList&gt;
        &lt;/div&gt;
    &lt;/asp:Panel&gt;
    &lt;div class="PageTitle"&gt;
        &lt;asp:Label ID="PageHeaderLabel" runat="server"&gt;&lt;/asp:Label&gt;
    &lt;/div&gt;
    &lt;div class="MainDiv"&gt;
        &lt;div style="text-align: center;"&gt;
            &lt;div class="PlaceHolder"&gt;
                &lt;table id="formTable"&gt;
                    &lt;tr&gt;
                        &lt;td&gt;
                            &lt;asp:UpdatePanel runat="server" ID="updatepanelCustomer" UpdateMode="Conditional"&gt;
                                &lt;ContentTemplate&gt;
                                    &lt;span class="boldLabelLong"&gt;Customer:&lt;/span&gt;&lt;br /&gt;
                                    &lt;asp:TextBox ID="CustomerNameTextBox" Width="200" runat="server"&gt;&lt;/asp:TextBox&gt;
                                    &lt;asp:HiddenField ID="IxCustomerHiddenField" runat="server" /&gt;
                                    &lt;asp:Button ID="customerTriggerbutton" runat="server" Text="Button" Style="display: none;" /&gt;
                                &lt;/ContentTemplate&gt;
                            &lt;/asp:UpdatePanel&gt;
                        &lt;/td&gt;
                        &lt;td&gt;
                            &lt;asp:UpdatePanel runat="server" ID="updatepanelProgram" UpdateMode="Conditional"&gt;
                                &lt;ContentTemplate&gt;
                                    &lt;span class="boldLabelLong"&gt;Program:&lt;/span&gt;&lt;br /&gt;
                                    &lt;asp:TextBox ID="ProgramNameTextBox" Width="200" runat="server"&gt;&lt;/asp:TextBox&gt;
                                    &lt;asp:Button ID="programTriggerbutton" runat="server" Text="Button" Style="display: none;" /&gt;
                                    &lt;asp:HiddenField ID="IxProgramHiddenField" runat="server" /&gt;
                                &lt;/ContentTemplate&gt;
                                &lt;Triggers&gt;
                                    &lt;asp:AsyncPostBackTrigger ControlID="customerTriggerbutton" EventName="Click" /&gt;
                                &lt;/Triggers&gt;
                            &lt;/asp:UpdatePanel&gt;
                        &lt;/td&gt;
                        &lt;td&gt;
                            &lt;asp:UpdatePanel runat="server" ID="updatepanelWorkPackage" UpdateMode="Conditional"&gt;
                                &lt;ContentTemplate&gt;
                                    &lt;span class="boldLabelLong"&gt;WorkPackage:&lt;/span&gt;&lt;br /&gt;
                                    &lt;asp:TextBox ID="WorkPackageNameTextBox" Width="200" runat="server"&gt;&lt;/asp:TextBox&gt;
                                    &lt;asp:HiddenField ID="IxWorkPackageHiddenField" runat="server" /&gt;
                                    &lt;asp:Button ID="workPackageTriggerbutton" runat="server" Text="Button" Style="display: none;" /&gt;
                                &lt;/ContentTemplate&gt;
                                &lt;Triggers&gt;
                                    &lt;asp:AsyncPostBackTrigger ControlID="programTriggerbutton" EventName="Click" /&gt;
                                &lt;/Triggers&gt;
                            &lt;/asp:UpdatePanel&gt;
                        &lt;/td&gt;
                        &lt;td&gt;
                            &lt;asp:UpdatePanel runat="server" ID="updatepanelActivity" UpdateMode="Conditional"&gt;
                                &lt;ContentTemplate&gt;
                                    &lt;span class="boldLabelLong"&gt;Activity:&lt;/span&gt;&lt;br /&gt;
                                    &lt;asp:TextBox ID="ActivityNameTextBox" Width="200" runat="server"&gt;&lt;/asp:TextBox&gt;
                                    &lt;asp:HiddenField ID="IxActivityHiddenField" runat="server" /&gt;
                                    &lt;asp:Button ID="activityTriggerbutton" runat="server" Text="Button" Style="display: none;" /&gt;
                                &lt;/ContentTemplate&gt;
                                &lt;Triggers&gt;
                                    &lt;asp:AsyncPostBackTrigger ControlID="workPackageTriggerbutton" EventName="Click" /&gt;
                                    &lt;asp:AsyncPostBackTrigger ControlID="activityTriggerbutton" EventName="Click" /&gt;
                                &lt;/Triggers&gt;
                            &lt;/asp:UpdatePanel&gt;
                        &lt;/td&gt;
                    &lt;/tr&gt;
                &lt;/table&gt;
            &lt;/div&gt;
            &lt;div class="PlaceHolder"&gt;
                &lt;asp:Label ID="TemplateLabel" Text="Template:" CssClass="ControlLabel" runat="server"&gt;&lt;/asp:Label&gt;
                &lt;asp:UpdatePanel runat="server" ID="updatepanelTemplate" UpdateMode="Conditional"&gt;
                    &lt;ContentTemplate&gt;
                        &lt;asp:DropDownList ID="TemplateSelectDropDownList" runat="server" Width="400" Visible="true"
                            AutoPostBack="true"&gt;
                        &lt;/asp:DropDownList&gt;
                        &lt;asp:HiddenField ID="IxTemplateHiddenField" runat="server" /&gt;
                    &lt;/ContentTemplate&gt;
                    &lt;Triggers&gt;
                        &lt;asp:AsyncPostBackTrigger ControlID="workPackageTriggerbutton" EventName="Click" /&gt;
                    &lt;/Triggers&gt;
                &lt;/asp:UpdatePanel&gt;
                &lt;asp:Panel ID="SustainPanelTemplateOwner" Visible="true" runat="server"&gt;
                    &lt;div&gt;
                        &lt;asp:Label ID="TemplateOwnerLabel" Text="Owner:" CssClass="ControlLabel" runat="server"&gt;&lt;/asp:Label&gt;
                        &lt;asp:TextBox ID="TemplateOwnerTextBox" CssClass="controlMargin" Width="400" runat="server"&gt;&lt;/asp:TextBox&gt;
                    &lt;/div&gt;
                &lt;/asp:Panel&gt;
                &lt;asp:HiddenField ID="IxDeliverableHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="IxReleaseActionHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="IxConfigHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="IxTemplateOwnerHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="TemplateSelectedSnameHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="TemplateOwnerSelectedsNameHiddenField" runat="server" /&gt;
                &lt;asp:HiddenField ID="DeliverableSelectedHiddenField" runat="server" /&gt;
                &lt;div&gt;
                    &lt;asp:Label ID="DeliverableLabel" CssClass="ControlLabel" runat="server" Text="Deliverable:"&gt;&lt;/asp:Label&gt;
                    &lt;asp:TextBox ID="DeliverableTextBox" CssClass="controlMargin" Width="400" runat="server"&gt;&lt;/asp:TextBox&gt;
                &lt;/div&gt;
                &lt;asp:Panel ID="SustainPanelConfig" Visible="true" runat="server"&gt;
                    &lt;div&gt;
                        &lt;asp:Label ID="ConfigurationLabel" runat="server" Text="Configuration:" CssClass="ControlLabel"&gt;&lt;/asp:Label&gt;
                        &lt;select id="ConfigurationSelect" class="controlMargin"&gt;
                            &lt;option&gt;&lt;/option&gt;
                        &lt;/select&gt;
                    &lt;/div&gt;
                &lt;/asp:Panel&gt;
                &lt;asp:Panel ID="SustainPanelRelease" Visible="true" runat="server"&gt;
                    &lt;div&gt;
                        &lt;asp:Label ID="ReleaseActionLabel" CssClass="ControlLabel" runat="server" Text="Release Action:"&gt;&lt;/asp:Label&gt;
                        &lt;asp:TextBox ID="ReleaseActionTextBox" CssClass="controlMargin" Width="400" runat="server"&gt;&lt;/asp:TextBox&gt;
                    &lt;/div&gt;
                &lt;/asp:Panel&gt;
                &lt;asp:Panel ID="SustainPanel" Visible="true" runat="server"&gt;
                    &lt;div class="SustainPanelControls"&gt;
                        &lt;div&gt;
                            &lt;asp:Label ID="ChangeLabel" Text="Change #: " runat="server"&gt;&lt;/asp:Label&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:TextBox ID="ChangeTextBox" Width="110" runat="server"&gt;&lt;/asp:TextBox&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:Label ID="SupplementLabel" Text="Supplement: " runat="server"&gt;&lt;/asp:Label&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:TextBox ID="SupplementTextBox" Width="80" runat="server"&gt;&lt;/asp:TextBox&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:Label ID="NewWrrLabel" Text="WRR #: " runat="server"&gt;&lt;/asp:Label&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:TextBox ID="NewWrrTextBox" Width="80" runat="server"&gt;&lt;/asp:TextBox&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:Label ID="DddLabel" Text="3D: " runat="server"&gt;&lt;/asp:Label&gt;
                        &lt;/div&gt;
                        &lt;div&gt;
                            &lt;asp:TextBox ID="DddTextBox" Width="80" runat="server"&gt;&lt;/asp:TextBox&gt;
                        &lt;/div&gt;
                    &lt;/div&gt;
                    &lt;div&gt;
                        &lt;table id="DesignDataTable2"&gt;
                            &lt;tr&gt;
                                &lt;td&gt;
                                    &lt;asp:Label ID="AllFbSheetsWrrLabel" Text="All F/B Sheets w/WRR #:" CssClass="ControlLabel" runat="server"&gt;&lt;/asp:Label&gt;
                                &lt;/td&gt;
                                &lt;td&gt;
                                    &lt;asp:TextBox CssClass="completeControl" ID="AllFbSheetsWrrTextBox" Width="588" Rows="2"
                                        TextMode="MultiLine" runat="server"&gt;&lt;/asp:TextBox&gt;
                                &lt;/td&gt;
                            &lt;/tr&gt;
                        &lt;/table&gt;
                    &lt;/div&gt;
                &lt;/asp:Panel&gt;
            &lt;/div&gt;
            &lt;div class="EditButtonGroup"&gt;
                &lt;input id="EditButton" type="button" value="Edit" class="ButtonSettings" /&gt;
                &lt;input id="RemoveButton" type="button" value="-" class="ButtonSettings" /&gt;
                &lt;input id="AddButton" type="button" value="+" class="ButtonSettings" /&gt;
            &lt;/div&gt;
        &lt;/div&gt;
        &lt;div class="ViewData"&gt;
            &lt;div class="ViewDataDiv"&gt;
                &lt;table id="DesignDataTable" class="designDataTable"&gt;
                    &lt;tbody&gt;
                    &lt;/tbody&gt;
                &lt;/table&gt;
            &lt;/div&gt;
        &lt;/div&gt;
        &lt;div class="submitButtonDiv"&gt;
            &lt;asp:Button ID="SubmitButton" runat="server" Text="Button Text" class="submitButtonCreateChecklist" /&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/asp:Content&gt;
</code></pre>
