Comment 9 for bug 174570

My problem, back in 2007, had to do with trying to change the proxy networking settings. As I recall, everything else would work just fine. My solution was to edit the synaptic configuration file manually.

Would you mind posting the contents of your synaptic configuration file? There might be a clue there. It's a text file located at:

        /root/.synaptic/synaptic.conf

Additionally, you can try to re-install synaptic. You can do this from the command line by typing in:

       sudo apt-get install synaptic dpkg