Comment 8 for bug 566710

I had the same issue, doing a fresh install of firebird2.1-classic on UNR10.04 (not an upgrade).
There was a defunct process with proctitle starting with firebird2.1-<something>, I had to kill that *and* its companion "frontend" process before synaptic would continue.
Manually running dpkg-reconfigure firebird2.1-classic reveals that it is attempting to ask me a question (whether I need the server running or not). Synaptic did not display any prompt of any sort; perhaps that was the problem (UI took a left turn into hyperspace, meanwhile dpkg still waiting for input)?