Can't Define Class Or Member That Utilizes Dynamic

I'm using Facebook SDK C# Library in Asp.Net 3.5 Application. When I'm trying to compile the code below give me the errors. As I know dynamic type using in 4.0 framework. So is anyway to rewrite it in order make it work? I have a reference to System.Core 3.5 but it's still not compiling

protected void Page_Load(object sender, EventArgs e)
{
if (Request.Params.AllKeys.Contains("signed_request"))
{
var result = FacebookSignedRequest.Parse(FacebookContext.Current.AppSecret, Request.Params["signed_request"]);
dynamic signedRequestValue = result.Data;
this.RegistrationData = signedRequestValue.registration;
}
else
{
Response.Redirect("~/");
}
}
protected dynamic RegistrationData { get; set; }

Error 1 Cannot define a class or member that utilizes 'dynamic' because the compiler required type 'System.Runtime.CompilerServices.DynamicAttribute' cannot be found. Are you missing a reference to System.Core.dll?

Error 2 Cannot define a class or member that utilizes 'dynamic' because the compiler required type 'System.Runtime.CompilerServices.DynamicAttribute' cannot be found. Are you missing a reference to System.Core.dll?