[arch-general] broken package stops pacstrap

Trying to install arch i686 on my IBM x345 using 2015 07 install media (yes I know its 2 years old). Get as far as running pacstrap and it comes to a crashing halt on checking package integrity error: krb5 : signature from "Levente Polyak (anthraxx) levente@leventepolyak.net> " is unknown trust :: File /mnt/var/cache/pacman/pkg/krb5-1.15.1-1-i686.pkg.tar.xz is corrupted (invalid or corrupted package PGP signature)). How can I get past this crash mick in glen innes