update complains about unsigned code

Attemted to uinstall latest Firefox update and was told I was tryiing to install Unsigned code. I canceled the update and asked it to refresh, and recived an "unexpected error" the details are as follows.

2216, in
main()
File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 2213, in main
run(args, options.single)
File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 2175, in run
backend.dispatcher(args)
File : /usr/lib/python2.6/dist-packages/packagekit/backend.py, line 699, in dispatcher
self.dispatch_command(args[0], args[1:])
File : /usr/lib/python2.6/dist-packages/packagekit/backend.py, line 606, in dispatch_command
self.refresh_cache(force)
File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 202, in _locked_cache
func(*args, **kwargs)
File : /usr/share/PackageKit/helpers/apt/aptBackend.py, line 1498, in refresh_cache
format_string(error.message))
File : /usr/lib/python2.6/dist-packages/packagekit/backend.py, line 723, in format_string
txt = unicode(text, encoding, errors='replace')

Please advise.
macd@core2blk:~$ lsb_release -rd
Description: Ubuntu 10.04.3 LTS
Release: 10.04

kpackagekit:
  Installed: 0.5.4-0ubuntu4.3
  Candidate: 0.5.4-0ubuntu4.3
  Version table:
 *** 0.5.4-0ubuntu4.3 0
        500 ftp://ftp.cs.mun.ca/pub/mirror/ubuntu/ lucid-updates/main Packages
        100 /var/lib/dpkg/status
     0.5.4-0ubuntu4 0
        500 ftp://ftp.cs.mun.ca/pub/mirror/ubuntu/ lucid/main Packages
cmacd@core2blk:~$