Failed update for ubuntu 12.04 LTS

[ralph]

I am getting the following error message during an update to my ubuntu 
12.04 LTS system.  I'm not running under KDE -- however I did download 
the kubuntu 13.04 iso to load onto another computer.  Why is the update 
looking for the kubuntu install disk.

error message follows:

   ":CD/DVD 'Kubuntu 13.04 _Raring Ringtail_ - Release i386 (20130424)' 
is required

      Please insert the above CD/DVD into the drive '/media/cdrom/' to 
install software packages from it."

Doing an apt-get update asks for the same disk as does booting to the 
startup rescue option.

The problem seems to be about files that have been locked by the 
original update call.

I do have a copy of the apt-get terminal message which I can send if you 
like -- it's somewhat long though.