LINQ To Entity - Inner Join issue

You do not need join if you have defined correctly navigation properties. And if you just need Name, do not retrieve full entity.

string[] UserTypes = new string[1];

using (Crypto_Entities entities = new Crypto_Entities())
{
    int User_ID_Integer = int.Parse(User_ID.Trim());

    var query = 
        from User in entities.Users
        where User.ID == User_ID_Integer
        select User.UserTypes.Name;

    var name = query.FirstOrDefault();
    if (name != null)
    {
        UserTypes[0] = name;
    }
}

If you use navigation property in query, EF automatically generates all needed joins. But if you just select whole entity without defining Include - EF will not load related data. It makes sense, because otherwise you may load almost whole database if there are a lot of relations.