TLS fails

[Frederik Bosch]

After getting my ACL right (thanks Dieter!), I have problems installing 
an official certificate. I bought a certificate at RapidSSL. Starting 
slapd gives me the following error.

TLS init def ctx failed: -69
This error is thrown in openldap 2.4.17. Since I am on debian, slapd is 
compiled against GnuTLS. When I was using 2.4.11 I had another error:

TLS init def ctx failed: -207

When I had a self-signed certificate I had no trouble. What could be wrong?