If any situation arises like Horde login is failed with the below error in the Apache log files, check for the ownership of files and directories under /var/cpanel/userhomes/cpanelhorde.

Error log in apache log file:

PHP Warning: Unknown: open(/var/cpanel/userhomes/cpanelhorde/sessions/sess_6f4fe8e66b99d89b239eb0839e3393a7, O_RDWR) failed: Permission denied (13) in Unknown on line 0
PHP 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
Steps used to solve the error:

#cd /var/cpanel/userhomes/cpanelhorde/
#chown -R cpanelhorde.cpanelhorde *
#tail -f /usr/local/cpanel/logs/error_log

Now, you will be able to login to the Horde email accounts.

If you require help, contact SupportPRO Server Admin