1) Backup horde database (/hordebackup.sql).

mysqldump -uadmin -p`cat /etc/psa/.psa.shadow` horde > horde_backup.sql

2) Run the below mysql queries for horde database.

mysql> select * from horde_prefs where pref_uid=’test@domain.com’ and pref_name=’sortpref’;

mysql> delete from horde_prefs where pref_uid=’test@domain.com’ and pref_name=’sortpref’;