Dolfin demo "No module named domains"

Hi,
I am just getting started with Fenics and Dolfin and therefore wanted to try the Dolfin demo "navier-stokes" in Python. However, when running it I get the following error:


python demo_navier-stokes.py 
Traceback (most recent call last):
  File "demo_navier-stokes.py", line 28, in 
    from dolfin import *
  File "/usr/lib/python2.7/dist-packages/dolfin/__init__.py", line 39, in 
    from dolfin.functions import *
  File "/usr/lib/python2.7/dist-packages/dolfin/functions/__init__.py", line 4, in 
    from dolfin.functions import function
  File "/usr/lib/python2.7/dist-packages/dolfin/functions/function.py", line 34, in 
    from dolfin.functions.constant import Constant
  File "/usr/lib/python2.7/dist-packages/dolfin/functions/constant.py", line 29, in 
    import ufl.domains
ImportError: No module named domains

I'm on Linux Mint 16 and I definitely have python-ufl installed. I've also tried uninstalling Fenics using

sudo apt-get purge fenics && /
sudo apt-get autoremove

and then reinstalling it again. I have also made sure that I'm using the Fenics PPA. Would anyone be able to help me with this problem?

Thanks!
Alexandra