When you are trying to open http://webmail.domain.tld to access IMP Webmail interface, the following error appears:
Registry objects should never be cloned.
This issue is caused by zend.ze1_compatibility_mode turned On. This setting is enabled on Fedora Core 4 by default. See for more information http://bugs.horde.org/ticket/?id=3463.
Switch zend.ze1_compatibility_mode Off in php.ini and restart Apache:
zend.ze1_compatibility_mode = Off