What is the most likely cause of the slapd daemon refuses to start when its init script is called.?

After modifying the indexes for a database in slapd.conf and running slapindex- the slapd daemon refuses to start

when its init script is called.
What is the most likely cause of this?

A.
The indexes are not compatible with the init script

B.
The init script is starting slapd as an ordinary user and the index files are owned by root

C.
The init script has identified one or more invalid indexes

D.
The init script can’t be run after executing slapindex, without first signing the indexes with slapsign