Since Apache version 2.2, the LDAP authentication module is no longer called auth_ldap, but rather authnz_ldap. During a migration of an Apache 2.0 to Apache 2.2, I ran into some problems which caused a failure to start Apache.
It seems that the configuration directive
AuthLDAPAuthoritative has been renamed to
AuthzLDAPAuthoritative, so you will have to replace these in your Apache config(s) - "sed" is your friend.
After replacing every occurrence of "AuthLDAPAuthoritative" in the Apache configuration files, I was able to start Apache, but there still seemed to be another issue. Pointing my browser to any of the vhosts with LDAP authentication enabled returned an internal server error (500). The Apache error log showed this: