cPanel Hosting Stuff

If Roundcube gives a blank page or any error please try the
below steps for a resolution.

Try following command
/usr/local/cpanel/bin/update-roundcube --force

if that did not help, make sure that

/usr/local/cpanel/3rdparty/bin/php and
/usr/local/cpanel/3rdparty/bin/php-cgi executable. otherwise do,

chmod 755 /usr/local/cpanel/3rdparty/bin/php-cgi
chmod 755 /usr/local/cpanel/3rdparty/bin/php

/scripts/makecpphp

if it is some database error, make sure that /tmp/mysql.sock is present.
If no, create symbolic link

ln -s /var/lib/mysql/mysql.sock /tmp/mysql.sock

Cpanel Basics