Are you sure the database directory (and all of its contents) for dc=mydomain,dc=org is writable by the user slapd runs as? Looks like it isn't ...
I've seen this numerous times with OpenLDAP 2.3.x and a hard failure. It usually indicates the alock file is in a corrupted state, preventing recovery and startup. Which is why I suggested what I did.
There's been several fixes to alock in 2.4, and I haven't seen this issue there so far.
--Quanah -- Quanah Gibson-Mount Principal Software Engineer Zimbra, Inc -------------------- Zimbra :: the leader in open source messaging and collaboration