Required Field Validation based on condition

I have a scenario, where user has to select any one role from radiobuttonlist to register himself as below

  • Administrator
  • Shop floor User
  • Key User
  • Others

If he selects Role "Others" from radio-button list, a text box will be appeared to enter the role manually. Can I have a RequiredFieldValidator for text-box if only user selects role "Others" else if he selects other roles validation is not required.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Required_Field_Validator_based._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<
body>
    <form id="form1" runat="server">
    <div>
    <table align="center">
            <tr>
                <td colspan="2">
                    <h3>
                       Registration Form</h3>
                </td>
            </tr>
            <tr>
                <td>
                    Name:</td>
                <td>
                    <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
                </td>
                <td><asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="Enter Name" ControlToValidate="txtName"></asp:RequiredFieldValidator> </td>
            </tr>
            <tr>
                <td>
                    Email</td>
                <td>
                    <asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
                </td>
                <td><asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ErrorMessage="Enter Email" ControlToValidate="txtEmail"></asp:RequiredFieldValidator> </td>
            <td> <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ErrorMessage="Invaid Email" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" ControlToValidate="txtEmail"></asp:RegularExpressionValidator> </td>
            </tr>
            <tr>

                <td>
                    Role</td>
                <td>
                    <asp:RadioButtonList ID="rbtRole" runat="server" RepeatDirection="Vertical"
                        AutoPostBack="True" onselectedindexchanged="rbtRole_SelectedIndexChanged">
                        <asp:ListItem>Administrator</asp:ListItem>
                        <asp:ListItem>Shop floor User</asp:ListItem>
                         <asp:ListItem>Key User</asp:ListItem>
                         <asp:ListItem>Others</asp:ListItem>
                    </asp:RadioButtonList>
                </td>
                 <td><asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ErrorMessage="Select role" ControlToValidate="rbtRole"></asp:RequiredFieldValidator> </td>
            </tr>
            <asp:Panel ID="panell" runat="server" Visible="false">
            <tr>
            <td></td><td><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></td>
            <td><asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="Enter role" ControlToValidate="TextBox1"></asp:RequiredFieldValidator> </td>

            </tr>
            </asp:Panel>
            <tr>
                <td align="center"  colspan="2">
                    <asp:Button ID="btn_register" runat="server"  Text="Register"

                       onclick="btn_register_Click" />

                 </td>
            </tr>
            <tr>
                <td align="center"  colspan="2">
                    <asp:Label ID="lblmsg" runat="server"></asp:Label>
                </td>
            </tr>
        </table>
    </div>
    </form>
</body>
</
html>

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
namespace Required_Field_Validator_based
{
    public partial class _Default : System.Web.UI.Page
    {
        string strConnString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlCommand com;

        protected void btn_register_Click(object sender, EventArgs e)
        {
            if (rbtRole.Text == "Others")
            {
                SqlConnection con = new SqlConnection(strConnString);
                com = new SqlCommand();
                com.Connection = con;
                com.CommandType = CommandType.Text;
                com.CommandText = "insert into login values(@Name,@Email,@role)";
                com.Parameters.Clear();
                com.Parameters.AddWithValue("@Name", txtName.Text);
                com.Parameters.AddWithValue("@Email", txtEmail.Text);
                com.Parameters.AddWithValue("@role", TextBox1.Text);
                if (con.State == ConnectionState.Closed)
                    con.Open();
                com.ExecuteNonQuery();
                con.Close();
                lblmsg.Text = "Data entered successfully!!!";
                clear();
            }
            else
            {
                SqlConnection con = new SqlConnection(strConnString);
                com = new SqlCommand();
                com.Connection = con;
                com.CommandType = CommandType.Text;
                com.CommandText = "insert into login values(@Name,@Email,@role)";
                com.Parameters.Clear();
                com.Parameters.AddWithValue("@Name", txtName.Text);
                com.Parameters.AddWithValue("@Email", txtEmail.Text);
                com.Parameters.AddWithValue("@role", rbtRole.SelectedValue);
                if (con.State == ConnectionState.Closed)
                    con.Open();
                com.ExecuteNonQuery();
                con.Close();
                lblmsg.Text = "Data entered successfully!!!";
                clear();
            }
          
        }

        protected void rbtRole_SelectedIndexChanged(object sender, EventArgs e)
        {
            lblmsg.Text = "";
 
            if (rbtRole.SelectedValue == "Others")
            {
                panell.Visible = true;
                TextBox1.CausesValidation = true;
            }
            else
            {
                panell.Visible = false;
                TextBox1.CausesValidation = false;
            }
        }
        private void clear()
        {
            TextBox1.Text = "";
            txtEmail.Text = "";
            txtName.Text = "";
            rbtRole.ClearSelection();
        }
    }
}