Cannot enable TLS for LDAP

My configuration (php 5.6, apache 2.4, Windows 10)

I use ldap_start_tls() function. I have add root cert to C:\OpenLDAP\sysconf\certs.

ldap.conf:
TLS_REQCERT demand
TLS_CACERT C:\OpenLDAP\sysconf\certs\root.pem

ldap_start_tls() return warning:
Warning (2): ldap_start_tls(): Unable to start TLS: Connect error

What's wrong, why function does return warning?

Thanks