I can't update the latest Webmin (1.590) and Usermin (1.510) from my Debian 5 server. I get the following message :
Installing package(s) with command apt-get -y install webmin .. Reading package lists... Building dependency tree... Reading state information... The following packages will be upgraded: webmin 1 upgraded, 0 newly installed, 0 to remove and 1 not upgraded. Need to get 18.2MB of archives. After this operation, 1430kB of additional disk space will be used. WARNING: The following packages cannot be authenticated! webmin E: There are problems and -y was used without --force-yes .. install failed!
The same update went fine on a Debian 6 server.