Ubuntu: invalid GPG signatures during apt-get update

If you get a message like the following while running apt-get update on Ubuntu:

W: GPG error: http://archive.ubuntu.com hardy-security Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key 

Try deleting the files in /var/lib/apt/lists/ (but leave the 'partial' directory alone) and running apt-get update again.

Source: update gpg error? - Ubuntu Forums

ntpd "Invalid argument" messages in log

I noticed that ntpd was generating a bunch of these messages in my logs.

Jan 14 06:05:14 starbug ntpd[5574]: sendto(xxx.xxx.xxx.xxx) (fd=22): Invalid argument
Jan 14 06:05:36 starbug ntpd[5574]: sendto(yyy.yyy.yyy.yyy) (fd=22): Invalid argument
Jan 14 06:05:40 starbug ntpd[5574]: sendto(zzz.zzz.zzz.zzz) (fd=22): Invalid argument

A quick Google search will tell you that this happens when your interface changes. In my case, my dynamic IP address from my ISP had changed. Restarting the ntpd service will correct the problem.