Background su XNA Game Studio

[HipT]

Ciao a tutti.
Vorrei sapere come posso inserire un background su un programma con xna game studio.Ora,riesco a visualizzare una texture ma devo visualizzare un background,
ho cercato alcuni esempi in internet,provato a inserire il codice nel mio programma ma mi da' degli errori...

Vi riporto il codice:

#region Using Statements
using System;
using System.Collections.Generic;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Storage;
#endregion

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    ContentManager content;
    //The 2D textures for the background
    Texture2D[] mBackgroundTexture = new Texture2D[1];

    //The X position of the background
    int mBackground1X = 0;


    //The object to draw the sprites 
    SpriteBatch mSpriteBatch;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        content = new ContentManager(Services);
        ////////////////////////////////
    }

    protected override void Initialize()
    {
        base.Initialize();
    }

    // This is a texture we can render.
    Texture2D sfondo,button1;

    // Set the coordinates to draw the sprite at.
    Vector2 posfondo = Vector2.Zero;
    Vector2 posbutton1 = Vector2.Zero;

    // This is the object that will draw the sprites.
    SpriteBatch spriteBatch;
    SpriteBatch imgbutton1Batch;


    protected override void LoadGraphicsContent(bool loadAllContent)
    {
        if (loadAllContent)
        {
            //mette a modalità finestra e imposta la risoluzione
            graphics.IsFullScreen = false;
            graphics.PreferredBackBufferHeight = 768;
            graphics.PreferredBackBufferWidth = 1024;
            graphics.ApplyChanges();   
            /////////////////////
            sfondo = content.Load<Texture2D>("416");
            spriteBatch = new SpriteBatch(graphics.GraphicsDevice);
            ///////////////
            imgbutton1Batch = new SpriteBatch(graphics.GraphicsDevice);
            button1 = content.Load<Texture2D>("entry");
        }
    }
    void LoadResources()
    {
        //Load the image into the texture object
        ContentManager aLoader = new ContentManager(Services);

        //Load the image into the texture object
        mBackgroundTexture[0] = aLoader.Load<Texture2D>("Background1") as Texture2D;

        //Set the starting "X" position for each of the background
        mBackground1X = 0;
        //Initialze the sprite batch object. This will be used to draw the sprite
        mSpriteBatch = new SpriteBatch(graphics.GraphicsDevice);
    }

    protected override void UnloadGraphicsContent(bool unloadAllContent)
    {
        if (unloadAllContent == true)
        {
            content.Unload();
        }
    }

    // Store some information about the sprite's motion.
    Vector2 spriteSpeed = new Vector2(50.0f, 50.0f);

    protected override void Update(GameTime gameTime)
    {
        // Allows the default game to exit on Xbox 360 and Windows.
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();
        base.Update(gameTime);
    }

    void UpdateSprite1(GameTime gameTime)
    {

    }

    protected override void Draw(GameTime gameTime)
    {
        graphics.GraphicsDevice.Clear(Color.CornflowerBlue);

        // Draw the sprite.
        spriteBatch.Begin(SpriteBlendMode.AlphaBlend);
        spriteBatch.Draw(sfondo, posfondo, Color.White);
        spriteBatch.End();
        ///////////////
        mSpriteBatch.Begin(SpriteBlendMode.Additive);
        mSpriteBatch.Draw(mBackgroundTexture[0], new Rectangle(mBackground1X, 0, this.Window.ClientBounds.Width, this.Window.ClientBounds.Height), Color.White);
        mSpriteBatch.End();
        ///////////////

        base.Draw(gameTime);
    }
}

L'errore me lo da' nel metodo "Draw",nell'ultima parte,quella compresa tra "/"
In debug non mi da' errori,solo in esecuzione si chiude tutto e mi segna la riga
"mSpriteBatch.Begin(SpriteBlendMode.Additive);" e se tolgo quella,le altre sotto...l'errore:"Riferimento a un oggetto non impostato su un'istanza di oggetto."

Come posso fare?
Questa cosa mi blocca di brutto...

Grazie.