You may have done it like that:
BookEntity book = new BookEntity();
book.Id = 27; //known book id existing in database; no need to fetch this entity to update fields
book.Title = "The Sphere";
string title = book.Title;
book.Author = "Michael Chrichton";
Adapter.SaveEntity(et);
MessageBox.Show("You just saved the following book: " + title);
The problem is that when you save an entity, many things could happen in the database, that the code can't be aware of, such as an identity field being set, or one or more triggers changing some fields values, you fieldr could have been altered by a trigger or so.
That's why an out of Sync exception is thrown when you use an entity that's not refetched.