library libz.so.1 missing

We try to install Sun Java Enterprise System Directory Server 6.0 on Redhat Enterprise Linux 4.0 (native Package).

Trying to initialize DSCC (dsccsetup initialize) we get the error message

[04/Jul/2007:16:17:15 +0200] - ERROR<4167> - Startup - conn=-1 op=-1 msgId=-1 - System error Load library /opt/ldap/server6/ds6/lib/replication-plugin.so: error libz.so.1: cannot open shared object file: No such file or directory

A library seems to be missing

ldd /opt/ldap/server6/ds6/lib/replication-plugin.so

shows

libz.so.1 => not found

$ find / -type f -name "libz.so.1*" shows

/usr/lib64/libz.so.1.2.1.2

Should there be a different one?

This is the package installed:

xlamucrh003:/etc $ rpm -q zlib

zlib-1.2.1.2-1.2

[799 byte] By [alpakaa] at [2007-11-27 10:42:42]