The log output that you pasted clearly instructed you to file a bug against 'update-manager'. Why was this filed against 'upgrade-system' instead?
-- Could not install libc6_2.4-1ubuntu12_i386.deb https://launchpad.net/bugs/71521 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
