Comment 2 for bug 1077598

The error in the log is:

Setting up initramfs-tools (0.99ubuntu13) ...
Installing new version of config file /etc/initramfs-tools/initramfs.conf ...
Installing new version of config file /etc/initramfs-tools/update-initramfs.conf ...
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools ...
update-initramfs: Generating /boot/initrd.img-2.6.32-45-generic
E: /usr/share/initramfs-tools/hooks/casper failed with return 1.
update-initramfs: failed for /boot/initrd.img-2.6.32-45-generic with 1.
dpkg: error processing initramfs-tools (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 initramfs-tools

This is probably a known (and since-fixed) bug in the casper hook. There is no reason to have the casper package on an installed system unless you're using a live image (which doesn't appear to be the case here); you should be able to work around this by removing the casper package.