Comment 11 for bug 450645

Yep, in your case, the problem is the existence of the "olcDatabase={1}hdb.ldif~" backup file.

(The postinst script currently assumes that only one file will contain the string "olcSuffix: dc=nasgul,dc=local", but here both the .ldif and .ldif~ file contain it.)

If you don't care much about keeping that backup file, you could delete it (or at least move it out of the slapd.d/cn=config directory), then run "dpkg --configure slapd" to try running the slapd configuration step again.

If you do want to keep the backup file, a workaround would be to rename it with a name that doesn't start with "olcDatabase" (e.g. "saved_olcDatabase={1}hdb.ldif~" or whatever).