scusate ho risolto...
è un bug e va risolto modificando questa riga in
/etc/httpd/conf.d/zz010_psa_httpd.conf:
php_admin_value include_path "/usr/share/psa-horde:/usr/share/psa-horde/pear:."
to:
php_admin_value include_path "/usr/share/psa-horde/lib:/usr/share/psa-horde:/usr/share/psa-horde/pear:."