up2date: package not signed with a GPG-key (aborting...)

["A.J. Bonnema" <abonnema xs4all nl>]

Sometimes I get a "package not signed with a gpg-key (aborting)" from 
up2date, which means I can't download these packages.

For instance, mplayer needs aalib, but aalib is not signed, so the 
download is aborted.

How can I go about getting this package signed or otherwise correct the 
issue?

Guus.
--
A.J. Bonnema, Leiden The Netherlands,
user #328198 (Linux Counter http://counter.li.org)