How to Implement Anti XSRF token in ASP.net 3.5

Question

i have added the Anti Xsrf Token code generated by VS 2012 in .Net web application in frame work 3.5, On Submission of any form in Application i got the error :

System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. http://go.microsoft.com/fwlink/?LinkID=314055 ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: Const AntiXsrfTokenKey As String = "__AntiXsrfToken" Const AntiXsrfUserNameKey As String = "__AntiXsrfUserName" Dim _antiXsrfTokenValue As String

Protected Sub Page_Init(sender As Object, e As System.EventArgs)
    ' The code below helps to protect against XSRF attacks
    Dim requestCookie As HttpCookie = Request.Cookies(AntiXsrfTokenKey)
    Dim requestCookieGuidValue As Guid
    If ((Not requestCookie Is Nothing) AndAlso Guid.TryParse(requestCookie.Value, requestCookieGuidValue)) Then
        ' Use the Anti-XSRF token from the cookie
        _antiXsrfTokenValue = requestCookie.Value
        Page.ViewStateUserKey = _antiXsrfTokenValue
    Else
        ' Generate a new Anti-XSRF token and save to the cookie
        _antiXsrfTokenValue = Guid.NewGuid().ToString("N")
        Page.ViewStateUserKey = _antiXsrfTokenValue

        Dim responseCookie As HttpCookie = New HttpCookie(AntiXsrfTokenKey) With {.HttpOnly = True, .Value = _antiXsrfTokenValue}
        If (FormsAuthentication.RequireSSL And Request.IsSecureConnection) Then
            responseCookie.Secure = True
        End If
        Response.Cookies.Set(responseCookie)
    End If

    AddHandler Page.PreLoad, AddressOf master_Page_PreLoad
End Sub

Private Sub master_Page_PreLoad(sender As Object, e As System.EventArgs)
    If (Not IsPostBack) Then
        ' Set Anti-XSRF token
        ViewState(AntiXsrfTokenKey) = Page.ViewStateUserKey
        ViewState(AntiXsrfUserNameKey) = If(Context.User.Identity.Name, String.Empty)
    Else
        ' Validate the Anti-XSRF token
        If (Not DirectCast(ViewState(AntiXsrfTokenKey), String) = _antiXsrfTokenValue _
            Or Not DirectCast(ViewState(AntiXsrfUserNameKey), String) = If(Context.User.Identity.Name, String.Empty)) Then
            Throw New InvalidOperationException("Validation of Anti-XSRF token failed.")
        End If
    End If
End Sub

i have disable ViewstateMac of pages in web config but still i got this error, i know disabling ViewStateMac is not good in security prospective. My application is hosted in web farm on production but not in local environment.