A hint for debugging bind failures in  your environment: many of the warnings PHP issues from this mehod begin "PHP Warning:  ldap_sasl_bind(): Unable to bind to server: [reason]" where [reason] can be a variety of strings. This makes it appear the failure originates with ldap_sasl_bind, but all [reason]s really come from the underlying c function ldap_sasl_interactive_bind_s. That function is used by lots of software besides php, so I've found a greater wealth of troubleshooting information by searching the web for "ldap_sasl_interactive_bind_s [reason]"