I was doing some server maintenance on one of my servers which houses a Plesk install. The base is Debian and a simple apt-get upgrade, as employed on plenty of previous occasions, updated the packages that needed updating.
Unfortunately, the sources.list for apt were configured to get the latest stable version and Debian 3.1 has recently moved to Debian 4 (etch). Unfortunately, as I have since found, Plesk 8.1 doesn't like etch and despite my best attempts to roll back the changes, all was in vain.
Better still, the admin functions that allow migration of accounts didn't work. So, I was left delving into the mysql psa database to regenerate the installation on another machine before migrating the /var/www/vhosts and /var/qmail/mailnames directories. That of course meant hand creating all clients, domains, email, forwards, aliases, subdomains.......... the list seems endless.
All my servers have now have their sources.list changed to getting 3.1 updates only. I'll not do that again.