=> When updating from a previous sks version be aware that the PGP key
=> database files are not compatible. You should run db_recover-5 on
=> the PTree and KDB database directories before starting SKS.

When installing for the first time, you will need to obtain a pgp
key database dump from somewhere and build database files from this.
http://www.keysigning.org/sks/ may help you getting started.