One more guide to fix this issue:

The webpage looks for the file /var/log/zimbra.log. It gets filled by sysklogd or syslog-ng. During installation, only one daemon gets modified. This depends on your $OS:

• SuSE: syslog-ng
• Ubuntu: sysklogd

So, if you are running Ubuntu and switch to syslog-ng, you won't see any new loglines within /var/log/zimbra.log. That can be another reason for the error in the subject. For more details, have a look at /opt/zimbra/bin/zmsyslogsetup.