You get the following error message in the LDAP event log:

Id                    : 1220
Message      : LDAP over Secure Sockets Layer (SSL) will be unavailable at this time because the server was unable to obtain a certificate.

               Additional Data
               Error value:
               8009030e No credentials are available in the security package

The reason

It is always a certificate problem.
However, there can be multiple reasons behind the same error message,
and all the following requirement have to be met.

Certificate requirements

• The LDAPS certificate is located in the
  Local Computer‘s Personal certificate store (programmatically known as the
  computer’s MY certificate store).
  Follow this link to see different ways to import a certificate into the Local
  Computer’s store

• A private key that matches the certificate is present in the Local Computer’s store and is correctly associated
  with the certificate.

• The private key strong protection has to be disabled.

  KeyProtection = NCRYPT_UI_NO_PROTCTION_FLAG

• The Enhanced Key Usage extension includes the Server Authentication (1.3.6.1.5.5.7.3.1) object identifier (also
  known as OID).

  [EnhancedKeyUsageExtension]
   OID=1.3.6.1.5.5.7.3.1 ; Server Authentication

  

• The certificate was issued by a CA that the domain controller and
  the LDAPS clients trust. Trust is
  established by configuring the clients and the server to trust the root CA
  to which the issuing CA chains.

• You must use the Schannel CSP to generate the key.

  ProviderName = "Microsoft RSA SChannel Cryptographic Provider"

  

• The Active Directory fully qualified domain name of the domain controller (for example, DC01.DOMAIN.COM) must
  appear in one of the following places:
  • The CN in the Subject field.
  • DNS entry in the Subject Alternative Name extension.

Note

This last requirement was the problem in my case.
I falsely assumed that having the DNS entry in
the Subject field was sufficient.
In fact, it must be both in the subject and also in the SAN
field. Furthermore, it must be the first one in the list.

More about

How
to enable LDAP over SSL with a third-party certification authority (KB321051)