Buildd.Net offers a buildd centric view to autobuilder network such as previously Debians autobuilder network or nowadays the autobuilder network of debian-ports.org. The policy of debian-ports.org requires a GPG key for the buildd to sign packages for upload that is valid for 1 year. Buildd admins are usually lazy people. At least they are running a buildd instead of building those packages all manually. Being a lazy buildd admin it might happen that you miss to renew your GPG key, which will render your buildd unable to upload newly built packages.
When participating in Buildd.Net you need to run update-buildd.net, a small script that transmits some statistical data about your package building. I added now a GPG key expiry check to that script that will warn the buildd admin by mail and text on the Buildd.Net arch status page, such as for m68k. So, either your client updates automatically to the new version or you can download the script yourself.