If you get Wrong ‘suhosin.session.encrypt’ option error after you install roundcube script on virtual domain, to solve the problem you must modify his value; from on to off in:
/etc/php5/apache2/conf.d/suhosin.ini:
; Transparent Encryption Options
;suhosin.session.encrypt = on
to
; Transparent Encryption Options
suhosin.session.encrypt = off
And then /etc/init.d/apache2 restart
I use Debian 6, by the way