DATABASE ERROR: CONNECTION FAILED
1) go to the folder /usr/local/cpanel/3rdparty/etc
there is a folder for application like horde, roundcube etc.
for horde , go to the folder /usr/local/cpanel/3rdparty/etc/roundcube
edit , php.ini and set
mysql.default_socket = /var/lib/mysql/mysql.sock
if you want you can make the same changes to horde etc.
2) /usr/local/cpanel/bin/update-roundcube –force