BURP-UI not working after clean install

I am trying to install BURP and BURP-UI on a fresh Debian 8 server. I followed every step listed in http://burp-ui.readthedocs.io/en/latest/step-by-step.html#burp2-server. After performing these steps, the UI is not reachable and the server is not listening on port 5000. (4971 and 4972 are listening).

Also when I issue the command "burp-ui" regardless of the switch used, I receive the following error:

Traceback (most recent call last):
  File "/usr/local/bin/burp-ui", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2876, in <module>
    working_set = WorkingSet._build_master()
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 451, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 464, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 639, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: cryptography>=1.3

I have also tried installing BURP separately following the steps listed here: http://burp.grke.org/docs/quickstart.html and then installing only BURP-UI by skipping the previous steps and starting at ``pip install --upgrade burp-ui`` in the Step by Step guide.

None of this has had any effect. How is it possible that a clean installation following every step as outlined on the website does not work?
I would like to know how to successfully install the newest versions of BURP and BURP-UI, BURP Is now at version 2.0.45 and I saw 0.4.0 for BURP-UI?

Thanks in advance.