I wrote a private message to the howto's author, Miguel, who told me he also had the same problem:
Originally Posted by Miguel
I'm sorry that I can't help you.
It worked when I wrote the How To.
It does work without the ACL's, but then postmasters cannot create email adresses, only the 'admin' (Openldap account can).
The syntax is correct, but there seems to be a truncated entry in the latest Openldap version. Even when trying to delete (ACL) with the line number option the error occurs (which shouldn't).
I haven't found a solution myself for the problem.
It seems there are some changes in the latest versions of openLDAP, configuration is no more made through the slapd.conf file (like it is shown in many documentations on the web), but directly in the config database.
Here is the openLDAP page about ldap browsers (useful to edit it): http://www.openldap.org/faq/data/cache/270.html