To get the log to generate, try raising the reporting level. Again in /usr/local/cpanel/base/horde/config/conf.php Change the following:
Code:
$conf['log']['priority'] = PEAR_LOG_WARN;
//change to
$conf['log']['priority'] = PEAR_LOG_DEBUG;
Is there a specific contact that always generates the blank page? For example, the name or email address. I've tried several different scenarios but have been unable to replicate it, which makes me think it's something very specific. If you could provide one or more examples of contacts that generate this problem it would help narrow down the issue.