apt-get update GPG error

I use apt-proxy several servers (no gui on any of them) on a machine 
called "david". I'm getting the error below on any machine that's set up 
for auto-update, but not on machines that are manually updated.

I suspect it has something to do with an attempted apt-get update while 
the proxy is off line, but I'm not sure. If I remove the proxy by way of 
editing the sources-list everything works again.

Google isn't helping me find a way of getting things to work again. Any 
suggestions how to fix it?


root@gary:~# apt-get update
Get:1 http://david precise Release.gpg [198 B]
Get:2 http://david precise-updates Release.gpg [198 B]
Get:3 http://david precise-backports Release.gpg [198 B]
Get:4 http://david precise-security Release.gpg [198 B]
Hit http://david precise Release
Ign http://david precise Release
E: GPG error: http://david precise Release: The following signatures 
were invalid: NODATA 1 NODATA 2

-- 
David McQuire
0418 310312

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