Well... I think it rebooted when I tried to install cadabra. Running "dpkg --configure -a" showed there were new stale files in /var/lib/dpkg/updates. Synaptic cannot be used until this is fixed although cadabra appeared to work.

So I moved the directory updates to updates_stale and made a new updates directory. I also copy back the files in update_stale to updates as the stale files will not copy

I then ran "dpkg --configure -a" again and got the message

set up /usr/lib/libpulsecommon-0.915 so that it is not a common link.
Synaptic works now.

Any ideas why this happens?

EDIT: Actually it is not working. I get an error concerning empty file name when trying to reinstall a file (texlive-latex-recommended-doc). I'm not allowed to proceed unless this is first fixed. I may have to start from scratch again...