Horde webmail agenda in Plesk is gone

Suddenly the agenda option in horde (psa-horde) is gone.

Cause:
If you’re using Atomick Rocket Turtle (ART) repository to update your server the agenda will not be available anymore, to solve this you have to remove it and update horde via the plesk updater available in the control panel.

Solution:

yum remove psa-kronolith

Log on to the control panel and go to server > updater and update your server.