When using the auth_ldap module with Apache 1.3, the log displays several messages containing "protocol error". Which of the following steps should be followed to fix the problem?

When the Apache `auth_ldap` module reports a "protocol error," particularly when interacting with an LDAP server that enforces or expects secure communication, it frequently means the TLS negotiation failed. Setting `AuthLDAPStartTLS On` explicitly instructs Apache to initiate a StartTLS operation, upgrading the plain LDAP connection to a secure TLS connection, which resolves these protocol-level communication errors.

Disallowing LDAPv2 (by setting `AuthLDAPVersion 3`) might be necessary for compatibility but typically wouldn't manifest as a "protocol error" related to secure connection negotiation.

Allowing LDAPv3 via `AuthLDAPVersion 3` ensures the correct protocol version is used, but a "protocol error" is more indicative of a security layer negotiation failure rather than a basic version mismatch.

The Apache module is configured in Apache's configuration files (e.g., `httpd.conf`), not in `slapd.conf`, which is the configuration file for the OpenLDAP server itself.

The `apache_auth.schema` defines attributes for LDAP entries used by Apache and is included in `slapd.conf` for the LDAP server, but its inclusion does not directly resolve a "protocol error" in the Apache client's connection attempt.