lembas,xkill surely closes the unresponsive task manager, but on reading its man pages I came to know it simply closes the connection with the server; eventhough most programs take a cue and terminate themselves, some programs continue to work.
There is no guarentee that xkill will always kill your task manager; what if it fails to do so?
It is better to use 'apt-get dist-upgrade' from a terminal until a permanent fix is made.
