I had the same problem, it was caused because I had installed python2.6. Removing the 'python' executable from /usr/local/bin (leaving only the identical python2.6 executable) fixed it, since 'python' now refers to the default ubuntu /usr/bin/python2.5.
I had the same problem, it was caused because I had installed python2.6. Removing the 'python' executable from /usr/local/bin (leaving only the identical python2.6 executable) fixed it, since 'python' now refers to the default ubuntu /usr/bin/python2.5.