Having done some research (i.e. googling the hell out of various combinations of that phrase) I was led to these two articles:
http://odzangba.wordpress.com/2009/10/14/how-to-fix-%E2%80%9Csubprocess-pre-removal-script-returned-error-exit-status-2%E2%80%B3-error/ and http://www.khattam.info/2009/08/04/solved-subprocess-pre-removal-script-returned-error-exit-status-2-error/comment-page-1/#comment-834
While both gave good advice, neither dealt with the specific error I had encountered.
sudo aptitude update"command followed by "
sudo aptitude -f install"did reveal a compile error installing the new packages.
With this in mind, I checked the version of python my machine was running with "python --version" which turned out to be 2.4. However, also installed are versions 2.6 and 3.2.
So, the version clearly needed to be changed. The existing python command line was removed with "sudo rm /usr/bin/python" and replaced with a new symlink to python 2.6 with "sudo ln -s /usr/bin/python2.6 /usr/bin/python"
Repeating the calls to aptitude revealed that this had indeed solved the problem, and I was able to upgrade successfully.
First step on the road completed.