Problem:
The previous upgrade failed to execute the postup.sh. To ensure everything in the postup.sh was executed successfully, the upgrade to the next UCS version is blocked. The postup.sh can be downloaded manually and re-executed.
Solution for UCS 4.4-5:
wget https://updates.software-univention.de/4.4/maintained/4.4-5/all/postup.sh
chmod +x postup.sh
./postup.sh && rm -f "/var/lib/univention-updater/univention-updater.status"
Solution for UCS 5.0-0:
wget https://updates.software-univention.de/dists/ucs500/postup.sh
chmod +x postup.sh
./postup.sh && rm -f "/var/lib/univention-updater/univention-updater.status"