SPClaimsUtility.AuthenticateFormsUser System.ServiceModel.FaultException`1 was unhandled by user code

Hi,

I am developing SharePoint 2010 application with custom login page based on Form Based Authentication. I am getting errorSPClaimsUtility.AuthenticateFormsUser System.ServiceModel.FaultException`1 was unhandled by user codewhen provides valid user information while login.

Below is code and exception traces.

CODE

using System;
using System.Web.UI;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.IdentityModel;
using Microsoft.SharePoint.IdentityModel.Pages;
namespace HFTECH_InventorySystem.Layouts.InventorySystem
{
    public partial class FBALogin : Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            this.btnLogin.Click += new EventHandler(btnLogin_Click);
        }
        void btnLogin_Click(object sender, EventArgs e)
        {
            string UserName = txtUserName.Text;
            string Password = txtPassword.Text;
            //string Domain = txtDomainName.Text;
            string siteUrl = "http://localhost:13928";
            Uri url = new Uri(SPContext.Current.Web.Url);
            bool ValidUser;
            ValidUser = SPClaimsUtility.AuthenticateFormsUser(url, UserName, Password);
            if (ValidUser)
                Response.Redirect(SPContext.Current.Web.Url);
            else
                lblError.Text = "Wrong UserID or Password.";
        }
    }
}

EXCEPTION

SPClaimsUtility.AuthenticateFormsUser System.ServiceModel.FaultException`1 was unhandled by user code
  Message=Object reference not set to an instance of an object.
  Source=Microsoft.IdentityModel
  Action=http://schemas.microsoft.com/net/2005/12/windowscommunicationfoundation/dispatcher/fault
  StackTrace:
       at Microsoft.IdentityModel.Protocols.WSTrust.WSTrustChannel.ReadResponse(Message response)
       at Microsoft.IdentityModel.Protocols.WSTrust.WSTrustChannel.Issue(RequestSecurityToken rst, RequestSecurityTokenResponse& rstr)
       at Microsoft.IdentityModel.Protocols.WSTrust.WSTrustChannel.Issue(RequestSecurityToken rst)
       at Microsoft.SharePoint.SPSecurityContext.SecurityTokenForContext(Uri context, Boolean bearerToken, SecurityToken onBehalfOf, SecurityToken actAs, SecurityToken delegateTo)
       at Microsoft.SharePoint.SPSecurityContext.SecurityTokenForFormsAuthentication(Uri context, String membershipProviderName, String roleProviderName, String username, String password)
       at Microsoft.SharePoint.IdentityModel.SPClaimsUtility.AuthenticateFormsUser(Uri context, String userName, String password)
       at IMP6101_InventorySystem.Layouts.InventorySystem.Login.btnLogin_Click(Object sender, EventArgs e)
       at System.Web.UI.WebControls.Button.OnClick(EventArgs e)
       at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument)
       at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)
       at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
  InnerException: 

Regards,

Mehar