Error when starting newrelic-daemon on freebsd 8.1

Question

I have installed the newrelic-deamon on our production environment but its won't start.

I get this error message when I tries to start it ( as root )

/libexec/ld-elf.so.1: Shared object "libz.so.4" not found, required by "newrelic-daemon"

What to do to fix this error ?