REASON!
Sudoers has been modified before the failed run... The sudo "as zimbra" pointers now point to directories that do not exist IF YOU HAVE RESTORED from backup...
OK. If you DID NOT try to install more than once, find the /etc/sudoersfile and repair (using visudo) to make "slapd start" work from zimbra user

You'll need to replace the references to openldap-2.x.x to openldap-2.y.y to match the restored file system, etc.
Now, if I can only fix my Referral limit issue...