Which packages did it say were unavailable?
Anyway, you should have a screenful of pluto packages, not just dcecommon.
One possibility is that apt-proxy, the software we use to cache all the debian packages that come from the Net, failed at some point while retrieving the listings. Did you see any "warning: could not get listing" messages? Still, the packages should have been drawn from our on-disk cache that the CD creates just before it reboots, unless you don't use the current version of the CD, in which case it will pull everything from the Net.
-- Edit --
In this case, choices are like this: you reattempt the installation; when you get a "package not available" or "package not found on any servers" error you go to a console and type "apt-get update" until none of the files fail. I'm still searching for a viable alternative/fix for this apt-proxy thing.