HTML Scraping with Python, document_fromstring is empty

I am trying to extract some data from a website using python. I found a (document that exactly fits to my problem.

But when I run the provided code

from lxml import html
import requests


page = requests.get('http://econpy.pythonanywhere.com/ex/001.html')
tree = html.fromstring(page.content)

#This will create a list of buyers:
buyers = tree.xpath('//div[@title="buyer-name"]/text()')
#This will create a list of prices
prices = tree.xpath('//span[@class="item-price"]/text()')


print 'Buyers: ', buyers
print 'Prices: ', prices

I get an error:

  File "C:Python27libsite-packageslxmlhtml__init__.py", line 617, in document_fromstring
    "Document is empty")

ParserError: Document is empty

Anyone an idea what the problem could be?