Slackpkg seems to be having problems finding files, even tho if correctly finds packages to upgrade. This is a typical output:
Resolving ftp.mirror.ac.uk... 18.104.22.168
Connecting to ftp.mirror.ac.uk|22.214.171.124|:21... connected.
Logging in as anonymous ... Logged in!
==> SYST ... done. ==> PWD ... done.
==> TYPE I ... done. ==> CWD /sites/ftp.slackware.com/slackware-current/slackware/xap ... done.
==> PASV ... done. ==> RETR mozilla-1.7.11-i486-1.tgz.asc ...
No such file `mozilla-1.7.11-i486-1.tgz.asc'.
md5sum: /var/cache/packages/mozilla-1.7.11-i486-1.tgz: No such file or directory
ERROR - Package not installed! gpg error!
I've tried a few different servers and 10.2 and current with same problem. Also it seems to have started around the time 10.2 came along.