The nss_afspag module assigns names to the fake groups that OpenAFS uses to store PAG information. This prevents the groups command from failing on a machine using OpenAFS PAGs, which can cause all sorts of annoying issues like WinSCP failing to work.

debathena% groups
mit sipb0 id: cannot find name for group ID 1091327919
debathena# sed 's/group: *compat/& afspag/' -i /etc/nsswitch.conf
debathena% groups
mit sipb0 afspag-1090650848

nss_afspag 1.0 was released on 2007-07-19, and is part of the Debian-Athena distribution. You can also browse and download the source.