I got a task to work with some files and I need to use NLTK. I work with Harry Potter books and short stories by J. K. Rowling. Some files are opened clerale, I can count words, sentences, etc., but I have a problem. When I try to open big files, I get something like this: https://pp.vk.me/c623420/v623420264/2d8b5/xE66_z6JWUs.jpg
Please, say what matter is.