When I try to run SSLstrip from the Terminal, I always get this error message, no matter what kind of command I try to run sslstrip with. Anybody knows how to resolve this?

Traceback (most recent call last):
File "/usr/bin/sslstrip", line 30, in <module>
from sslstrip.StrippingProxy import StrippingProxy
File "/usr/lib/python2.5/site-packages/sslstrip/StrippingProxy.py", line 20, in <module>
from ClientRequest import ClientRequest
File "/usr/lib/python2.5/site-packages/sslstrip/ClientRequest.py", line 25, in <module>
from twisted.internet import ssl
File "/usr/lib/python2.5/site-packages/twisted/internet/ssl.py", line 47, in <module>
from OpenSSL import SSL
ImportError: No module named OpenSSL