Xamarin Error Build FAILED: Unsupported major.minor version 52,0

I'm using Xamarin Visual Studio Comunti 2015 After compiling a project, however I get the following err:

Exception in thread "main" 
1>java.lang.UnsupportedClassVersionError: com/android/dx/command/Main  :  Unsupported major.minor version 52.0
1>Build FAILED.
1>
========== Deploy: 0 succeeded, 1 failed, 0 skipped ========== 

Code

using System; 
using Android.App; 
using Android.Content; 
using Android.Runtime; 
using Android.Views; 
using Android.Widget; 
using Android.OS;


namespace Calculadora {
    [Activity(Label = "Calculadora", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        EditText edtValor;
        Button btnCalcular;
        TextView txtGorjeta;
        TextView txtValorTotal;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView (Resource.Layout.Main);

            edtValor        = FindViewById<EditText>(Resource.Id.edtValor);
            btnCalcular     = FindViewById<Button>(Resource.Id.btnCalcular);
            txtGorjeta      = FindViewById<TextView>(Resource.Id.txtGorjeta);
            txtValorTotal   = FindViewById<TextView>(Resource.Id.txtValorTotal);

            btnCalcular.Click += btnCalcular_Click;

        }


        void btnCalcular_Click(object sender,EventArgs e)
        {
            double valor = 0;
            valor = double.Parse(edtValor.Text);
            double valorTotal = 0;

            valor = valor * .10;
            valorTotal = valorTotal + valor;
            txtGorjeta.Text = valor.ToString();
            txtValorTotal.Text = valorTotal.ToString();
        }
    } }