System.Web.HttpException: Unable to find control id 'txtDob' referenced by the 'ControlToValidate' property of 'RequiredFieldValidator5'.

Question

i hv got error in this code below..plz give solution.
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;
using System.Data.OleDb;
public partial class _Default: System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)
    //declaring connection string and command
    //here we are extracting connection string from web.config file
    OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\WebSite5\App_Data\db.accdb");
    protected void btnSubmit_Click(object sender, EventArgs e)
        if
(!Page.IsPostBack)
            //Fill Years
            for (int i = 2013; i <= 2020; i++)
                ddlYear.Items.Add(i.ToString());
            ddlYear.Items.FindByValue(System.DateTime.Now.Year.ToString()).Selected = true;  //set current year as selected
            //Fill Months
            for (int i = 1; i <= 12; i++)
                ddlMonth.Items.Add(i.ToString());
            ddlMonth.Items.FindByValue(System.DateTime.Now.Month.ToString()).Selected = true; // Set current month as selected
            //Fill days
            FillDays();
    public void FillDays()
        ddlDay.Items.Clear();
        //getting numbner of days in selected month & year
        int noofdays = DateTime.DaysInMonth(Convert.ToInt32(ddlYear.SelectedValue), Convert.ToInt32(ddlMonth.SelectedValue));
        //Fill days
        for (int i = 1; i <= noofdays; i++)
            ddlDay.Items.Add(i.ToString());
        ddlDay.Items.FindByValue(System.DateTime.Now.Day.ToString()).Selected = true;// Set current date as selected
    protected void ddlYear_SelectedIndexChanged(object sender, EventArgs e)
        FillDays();
    protected void ddlMonth_SelectedIndexChanged(object sender, EventArgs e)
        FillDays();
        try
            con.Open();
            OleDbCommand cmd = new OleDbCommand("INSERT INTO UserDetails values(@Fname,@Lname,@Email,@Password,@Gender,@Dob,@Mobile,@Address)",con);
            //cmd.Connection = con; //assigning connection to command
            //cmd.CommandType = CommandType.Text; //representing type of command
            //cmd.CommandText = "INSERT INTO UserDetails (Fname,Lname,Email,Password,Gender,Dob,Mobile,Address) values
            // (@Fname,@Lname,@Email,@Password,@Gender,@Dob,@Mobile,@Address)";
            //cmd.CommandText = "INSERT INTO UserDetails values(@Fname,@Lname,@Email,@Password,@Gender,@Dob,@Mobile,@Address)";
            //adding parameters with value
            cmd.Parameters.AddWithValue("@Fname", txtFirstName.Text.ToString());
            cmd.Parameters.AddWithValue("@Lname", txtLastName.Text.ToString());
            cmd.Parameters.AddWithValue("@Email", txtEmail.Text.ToString());
            cmd.Parameters.AddWithValue("@Password", txtPassword.Text.ToString());
            cmd.Parameters.AddWithValue("@Gender", RdoGender.SelectedItem.Text.ToString());
            cmd.Parameters.AddWithValue("@Dob", ( ddlDay.SelectedIndex+ddlMonth.SelectedIndex+ddlYear.SelectedIndex).ToString());
            cmd.Parameters.AddWithValue("@Mobile", txtMobile.Text.ToString());
            cmd.Parameters.AddWithValue("@Address", txtAddress.Text.ToString());
            //con.Open(); //opening connection
            cmd.ExecuteNonQuery();  //executing query
            con.Close(); //closing connection
            lblMsg.Text = "Registered Successfully..";
        catch (Exception ex)
            lblMsg.Text = ex.Message.ToString();
    protected void btnClear_Click(object sender, EventArgs e)
        //refreshing/reloading page to clear all the controls
        Page.Response.Redirect(Page.Request.Url.ToString(), true);
and my web.conf code is below:
<?xml version="1.0"?>
<!--
    Note: As an alternative to hand editing this file you can use the
    web admin tool to configure settings for your application. Use
    the Website->Asp.Net Configuration option in Visual Studio.
    A full list of settings and comments can be found in
    machine.config.comments usually located in
    \Windows\Microsoft.Net\Framework\v2.x\Config
-->
<configuration>
    <configSections>
      <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
        <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
          <section name="scriptResourceHandler" type="System.Web.Configuration.ScriptingScriptResourceHandlerSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
requirePermission="false" allowDefinition="MachineToApplication"/>
          <sectionGroup name="webServices" type="System.Web.Configuration.ScriptingWebServicesSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
            <section name="jsonSerialization" type="System.Web.Configuration.ScriptingJsonSerializationSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
requirePermission="false" allowDefinition="Everywhere" />
            <section name="profileService" type="System.Web.Configuration.ScriptingProfileServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
requirePermission="false" allowDefinition="MachineToApplication" />
            <section name="authenticationService" type="System.Web.Configuration.ScriptingAuthenticationServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
requirePermission="false" allowDefinition="MachineToApplication" />
            <section name="roleService" type="System.Web.Configuration.ScriptingRoleServiceSection, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
requirePermission="false" allowDefinition="MachineToApplication" />
          </sectionGroup>
        </sectionGroup>
      </sectionGroup>
    </configSections>  
    <appSettings/>
    <connectionStrings>
        <add name="ConnectionString" connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\WebSite5\App_Data\db.accdb"
            providerName="System.Data.OleDb" />
    </connectionStrings>
    <system.web>
        <!--
            Set compilation debug="true" to insert debugging
            symbols into the compiled page. Because this
            affects performance, set this value to true only
            during development.
        -->
        <compilation debug="false">
          <assemblies>
            <add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
            <add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
            <add assembly="System.Data.DataSetExtensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
            <add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
          </assemblies>
        </compilation>
        <!--
            The <authentication> section enables configuration
            of the security authentication mode used by
            ASP.NET to identify an incoming user.
        -->
        <authentication mode="Windows" />
        <!--
            The <customErrors> section enables configuration
            of what to do if/when an unhandled error occurs
            during the execution of a request. Specifically,
            it enables developers to configure html error pages
            to be displayed in place of a error stack trace.
        <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
            <error statusCode="403" redirect="NoAccess.htm" />
            <error statusCode="404" redirect="FileNotFound.htm" />
        </customErrors>
        -->
      <pages>
        <controls>
          <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
          <add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        </controls>
      </pages>
      <httpHandlers>
        <remove verb="*" path="*.asmx"/>
        <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"
validate="false"/>
      </httpHandlers>
      <httpModules>
        <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      </httpModules>
    </system.web>
    <system.codedom>
      <compilers>
        <compiler language="c#;cs;csharp" extension=".cs" warningLevel="4"
                  type="Microsoft.CSharp.CSharpCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
          <providerOption name="CompilerVersion" value="v3.5"/>
          <providerOption name="WarnAsError" value="false"/>
        </compiler>
        <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" warningLevel="4"
                  type="Microsoft.VisualBasic.VBCodeProvider, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
          <providerOption name="CompilerVersion" value="v3.5"/>
          <providerOption name="OptionInfer" value="true"/>
          <providerOption name="WarnAsError" value="false"/>
        </compiler>
      </compilers>
    </system.codedom>
    <!--
        The system.webServer section is required for running ASP.NET AJAX under Internet
        Information Services 7.0.  It is not necessary for previous version of IIS.
    -->
    <system.webServer>
      <validation validateIntegratedModeConfiguration="false"/>
      <modules>
        <remove name="ScriptModule" />
        <add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      </modules>
      <handlers>
        <remove name="WebServiceHandlerFactory-Integrated"/>
        <remove name="ScriptHandlerFactory" />
        <remove name="ScriptHandlerFactoryAppServices" />
        <remove name="ScriptResource" />
        <add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode"
             type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode"
             type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add name="ScriptResource" preCondition="integratedMode" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions,
Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
      </handlers>
    </system.webServer>
    <runtime>
      <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
          <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35"/>
          <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
        </dependentAssembly>
        <dependentAssembly>
          <assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35"/>
          <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="3.5.0.0"/>
        </dependentAssembly>
      </assemblyBinding>
    </runtime>
</configuration>

Answer 1

Hi,
This error must be generated from any of the ".aspx" page.
As,error clearly mentions 
control "txtDob" not found. It means you definitely dont have this control present on your page, Or you renamed it to some other Name.
To resolve this error,
1) Search for text box (i think in your case Date of birth) take name of that textbox
2) Assign same textbox name in  "RequiredFieldValidator5" Property "ControlToValidate"
Regards