I have getting the error while installing zimbra

OS Version : Ubuntu 8.04.1 LTS Server Edition
Zimbra Version : zcs-5.0.10_GA


Fri Nov 21 08:01:49 2008 Operations logged to /tmp/zmsetup.11212008-080127.log
Fri Nov 21 08:01:49 2008 checking isEnabled zimbra-ldap
Fri Nov 21 08:01:49 2008 zimbra-ldap is enabled
Fri Nov 21 08:01:49 2008 Initializing ldap...
Fri Nov 21 08:01:49 2008 *** Running as zimbra user: /opt/zimbra/libexec/zmldapinit
IO::Socket::INET: connect: Connection refused at /opt/zimbra/libexec/zmldapinit line 160.
Fri Nov 21 08:02:30 2008 failed. (28416)
Fri Nov 21 08:02:30 2008

ERROR

Fri Nov 21 08:02:30 2008

Configuration failed

Fri Nov 21 08:02:30 2008 Please address the error and re-run /opt/zimbra/libexec/zmsetup.pl to
Fri Nov 21 08:02:30 2008 complete the configuration.
Fri Nov 21 08:02:30 2008
Errors have been logged to /tmp/zmsetup.11212008-080127.log