Key warning

[David Ryder]

Hi,
I have just done an apt-get update after adding
deb http://ppa.launchpad.net/jeffreyratcliffe/ubuntu <release> main
to my souces.list and adding the key
gpg --keyserver subkeys.pgp.net --recv-keys 4DD7CC93
gpg --export --armor 4DD7CC93 | sudo apt-key add -
to my keyring ( as per http://gscan2pdf.sourceforge.net/ ).

The results of the apt-get update were OK until the end when this
happens:
...
Hit http://au.archive.ubuntu.com hardy-security/multiverse Packages
Fetched 309B in 3s (88B/s)
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net hardy Release: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY C5E6A5ED249AD24C
W: You may want to run apt-get update to correct these problems

I deleted the jeffreyratcliffe key from the keyring but the warning
still occurs. Looking in synaptic, the apt-get update has not retrieved 
the latest version which I believe it should (and the website says).

Have I misinterpreted the warning and assumed it was the key I added /
deleted? If so, how can I find out what it refers to as nothing like it
appears in my keyring?

Many thanks,
David