The update manager is still stuck in updating the linux kernel (linux-image-2.6.35-24-generic) in the process of updating the grub entries. I think the problem is that the update manager doesn't have root privileges to continue (the app indicator with the key icon disappeared) and I want to know if it's safe to kill the update manager and start the process over.
It is safe to kill update-manager, but after that please run the following:
sudo dpkg --configure -a sudo apt-get install -f sudo apt-get update && sudo apt-get upgrade
I ran into the same issue, and found a solution that worked for me based on: linuxquestions.org
Execute the following commands:
ps -e | grep apt
sudo kill -9 <pid>
For each apt/aptd pid reported.