Environment:
FreeBSD 10.1-RELEASE-p8 i386

Problem:

• FreeBSD repository is up-to-date & all repositories are up-to-date, but when I try to install some package, it’ll try to fetch the non-latest version(so … 404 not found)
• Keep getting message like this : pkg: cached package bind-tools-9.10.2: size mismatch, fetching from remote
• pkd version said that there are some out-date packages, but pkg upgrade said every thing is up-to-update

pkg update -> not working
pkg clean + pkg update -> still not working
reboot -> of course not working …

So I did this to clean its cache:
$ sudo rm -rf /var/cache/pkg/*
and force update
$ sudo pkg update -f

Fortunately, it works fine now.