Allright, First of all, thank your for your answers.So I found the solution at http://lists.debian.org/debian-glibc/2002/10/msg00538.html
The getpwnam function seems to need all the /lib/libnss_* in the chroot jail.
I also put in the chroot jail the needed shared libraries by slapd We can see the list with `ldd /usr/local/openldap/libexec/slapd` Fabien.
