Sophos Anti-Virus for Linux, version 6, is failing to update on Ubuntu 8.04 on 64-bit systems.
Sophos product and version
Sophos Anti-Virus for Linux, version 6.x.x
Ubuntu 8.04 running on any 64-bit-based system
What to do
The 64-bit version of Ubuntu 8.04 does not include a 32-bit compatibility library for DNS.
Install the 32-bit compatibility library of libnss-mdns.