Slapd service won't start, unable to open pid file
What distribution are you running and how did you install OpenLDAP?
The error you got is from AppArmor and tells you that it prevented slapd from creating it's pid file.
For Ubuntu: You should have something like the following in your /etc/apparmor.d/usr.bin.slapd file:
/{,var/}run/ldap/* w,
to allow this.
Normally, this should be set up to work without further configuration.