MVC 4 code first database initializer doesn't work

I had to stop at the same stages following different MVC 4 code first technique tutorials, because database initialization failed.

Using the connection

<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=aspnet-DbTestApp-20130205173443;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnet-DbTestApp-20130205173443.mdf" providerName="System.Data.SqlClient" />

I can't even create or manage the database, which I want to be generated from my models

public class Category
    {
        public int Id { get; set; }

        [Required]
        [MinLength(4)]
        [MaxLength(64)]
        public string Name { get; set; }

        public virtual IEnumerable<Article> Articles { get; set; }
    }

    public class Article
    {
        public int Id { get; set; }

        public int CategoryId { get; set; }
        public virtual Category Category { get; set; }

        [Required]
        [MinLength(4)]
        [MaxLength(64)]
        public string Title { get; set; }

        [Required]
        [MinLength(16)]
        [MaxLength(1024)]
        [DataType(DataType.MultilineText)]
        public string Content { get; set; }

        [Required]
        [Display(Name = "Post Anonymous?")]
        public bool IsAnonymous { get; set; }

        public int AuthorId { get; set; }
        public virtual Author Author { get; set; }

        public virtual IEnumerable<Comment> Comments { get; set; }

    }

    public class Author
    {
        public int Id { get; set; }

        [MinLength(3)]
        [MaxLength(64)]
        public string AuthorName { get; set; }

        public virtual IEnumerable<Article> Articles { get; set; }

        public virtual IEnumerable<Category> Categories { get; set; }
    }

    public class Comment
    {
        public int Id { get; set; }

        public int ArticleId { get; set; }
        public virtual Article Article { get; set; }

        [Required]
        [MinLength(3)]
        [MaxLength(64)]
        public string Author { get; set; }

        [MaxLength(64)]
        public string Title { get; set; }

        [Required]
        [MinLength(4)]
        [MaxLength(512)]
        public string Content { get; set; }
    }

using the context below

    public class BlogContext : DbContext
    {
        public DbSet<Category> Categories { get; set; }
        public DbSet<Article> Articles { get; set; }
        public DbSet<Author> Authors { get; set; }
        public DbSet<Comment> Comments { get; set; }

        public BlogContext()
            : base("DefaultConnection")
        {
            Configuration.ProxyCreationEnabled = false;
        }
    }

I also set the initializer in Global.asax Application_Start() method:

Database.SetInitializer(new DropCreateDatabaseIfModelChanges<BlogContext>());

The problem comes when I'm trying to call

var articles = db.Articles.Include(a => a.Category).Include(a => a.Author);

inside my BlogController's Index() method to return a view with the list of stored articles. That happens every time calling a DB related methods, the error message is:

Model compatibility cannot be checked because the database does not contain model metadata. Model compatibility can only be checked for databases created using Code First or Code First Migrations.

In the tutorials I found nothing about problems like that and the solutions I read couldn't solve the problem.

Any ideas?

Thanks