Problem
During an upgrade (i.e. from 4.1-x to 4.2-5) the UCS server claims it is not completely configured dyes and you are forced to run configuration wizard (which will wipe all current data!).
Solution
Check if the package “univention-system-boot” is installed on your server. If so remove it by using dpkg (or apt):
dpkg -r univention-system-boot
Reboot your server then.