If you are getting Horde login error in Cpanel like :
Warning: Unknown: write failed: Disk quota exceeded (122) in Unknown on line 0
Warning: Unknown: Failed to write session data (files). Please verify that the current setting of
session.save_path is correct (/var/cpanel/userhomes/cpanelhorde/sessions) in Unknown on line 0
Then try this Cpanel script :
/scripts/autorepair phpapps_owner_fix
The above script will reset all the quotas for the Cpanel* users.